PAL was funded by a Parkinson's UK Research Fellowship (grant F1002). This work was supported by a MRC New Investigator Research Grant (MR/L010933/1) and by MRC Programme grant MR/N026004/1 to PAL, and by BBSRC studentship BB/M017222/1 to JET. We thank the 2014-15 cohort of MPharm Part 1 students at the University of Reading for taking part in the first iteration of this practical, and subsequent cohorts for their feedback and input.

NOTE: The protocol below was developed to be held over the course of two hours (including completion of in-class worksheets) in a purpose-built teaching laboratory. The experimental steps were deliberately put together to exclude more detailed analysis of enzyme kinetics (carried out in the context of this course using model data); however &#8212; as noted in the discussion &#8212; the protocol provides a template for more advanced analyses depending upon time, facilities and student attainment level.
SAFETY: This practical should be carried out according to the rules of Good Chemical Laboratory Practice (GCLP) &#8212; personal protective equipment, including fastened laboratory coat, disposable gloves and safety glasses should be worn at all times in the laboratory.
1. Extracting the Enzyme
<ol>
	<li>Crush one lactase tablet, containing 200 mg of enzyme, to an even powder using a mortar and pestle.</li>
	<li>Place the resulting powder into a 15 mL tube labelled &#34;suspension&#34; and resuspend in 10 mL of 100 mM phosphate buffered saline (PBS).</li>
	<li>Vortex for 1 min to maximize enzyme extraction.</li>
	<li>Transfer 1 mL from the suspension into a 1.5 mL centrifuge tube and centrifuge for 1 min at 10,000 x g to sediment solid particles.</li>
	<li>Transfer 500 &#181;L of the supernatant to a clean 1.5 mL tube labelled &#34;Lactase Extract&#34;.</li>
</ol>
2. Observing the Colorimetric Reaction
<ol>
	<li>Place 390 &#181;L of 100 mM PBS into a 1.5 mL tube labelled &#34;Reaction A&#34;.</li>
	<li>Add 100 &#181;L of 5 mM ONPG solution and mix well by vortexing. 
	CAUTION: This practical uses ortho-Nitrophenol-beta-D-galactopyranoside (ONPG) as a substitute for lactose. Since ONPG is a phenolic compound, it should be handled with caution. In the event of skin contact with ONPG, the exposed skin should be washed immediately. Any spills should be wiped up immediately with paper towels to be disposed of into the appropriate waste stream.</li>
	<li>Add 10 &#181;L of extract into the reaction A tube and mix well by vortexing.</li>
	<li>Observe the reaction mixture for 5 minutes and note any colorimetric changes to the solution.</li>
</ol>
3. Measuring Enzyme Activity
<ol>
	<li>Set up two 1.5 mL tubes: one labelled &#34;Reaction B&#34;, one labelled &#34;Control&#34;.</li>
	<li>Add 390 &#181;L of 100 mM PBS to the reaction B tube, 400 &#181;L of 100 mM PBS to the control tube and then add 100 &#181;L of 5 mM ONPG to each tube.</li>
	<li>Mix the contents by vortexing.</li>
	<li>Add 10 &#181;L of lactase extract to the reaction B tube, mix by vortexing and allow the reaction to proceed for 1 min at room temperature.</li>
	<li>Once 1 min has elapsed, add 500 &#181;L of 1 M sodium carbonate to both tubes to inhibit the lactase enzyme by increasing the pH, thereby terminating the reaction.</li>
	<li>Transfer 500 &#181;L from each tube into clean spectrophotometer cuvettes and measure absorbance at 420 nm using the spectrophotometer.</li>
	<li>Note absorbance for reaction B and control samples, and then subtract the control value from the reaction value to derive the change in absorbance due to hydrolysis of ONPG in the presence of active enzyme.</li>
</ol>
4. Effect of Temperature on Enzyme Activity
<ol>
	<li>Set up three control tubes and three reaction tubes as described in section 3 and label these &#34;4 &#176;C&#34;, &#34;Room Temp&#34;, and &#34;37 &#176;C&#34;.</li>
	<li>Following addition of enzyme extract, incubate one tube on ice, one at room temperature, and one at 37 &#176;C (in a pre-heated water bath).</li>
	<li>Allow the reactions to proceed for 1 min and then terminate the reaction by adding 500 &#181;L of 1 M sodium carbonate to each tube.</li>
	<li>Measure the absorbance at 420 nm for each tube as described in section 3. Record the values, subtracting the control value from the reaction value in each case.</li>
</ol>

<ol>
	<li>Berg, J. M., Tymoczko, J. L., Gatto, J. G., Stryer, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Biochemistry. , (2015).</li><li>Jittam, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Red+seaweed+enzyme-catalyzed+bromination+of+bromophenol+red:+An+inquiry-based+kinetics+laboratory+experiment+for+undergraduates.">Red seaweed enzyme-catalyzed bromination of bromophenol red: An inquiry-based kinetics laboratory experiment for undergraduates.</a> Biochemistry and Molecular Biology Education. 37, 99-105 (2009).</li><li>Troelsen, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adult-type+hypolactasia+and+regulation+of+lactase+expression.">Adult-type hypolactasia and regulation of lactase expression.</a> Biochimica et biophysica acta. 1723, 19-32 (2005).</li><li>Juers, D. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+structural+view+of+the+action+of+Escherichia+coli+(lacZ)+beta-galactosidase.">A structural view of the action of Escherichia coli (lacZ) beta-galactosidase.</a> Biochemistry. 40, 14781-14794 (2001).</li><li>Plimmer, R. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+presence+of+lactase+in+the+intestines+of+animals+and+on+the+adaptation+of+the+intestine+to+lactose.">On the presence of lactase in the intestines of animals and on the adaptation of the intestine to lactose.</a> Journal of Physiology. 35, 20-31 (1906).</li><li>Krebs, H. A., Salvin, E., Johnson, W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+formation+of+citric+and+alpha-ketoglutaric+acids+in+the+mammalian+body.">The formation of citric and alpha-ketoglutaric acids in the mammalian body.</a> The Biochemical journal. 32, 113-117 (1938).</li><li>Vesa, T. H., Marteau, P., Korpela, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lactose+intolerance.">Lactose intolerance.</a> Journal of the American College of Nutrition. 19, 165S-175S (2000).</li><li>Robayo-Torres, C. C., Nichols, B. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+differentiation+of+congenital+lactase+deficiency+from+adult-type+hypolactasia.">Molecular differentiation of congenital lactase deficiency from adult-type hypolactasia.</a> Nutrition Reviews. 65, 95-98 (2007).</li><li>Swallow, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetics+of+lactase+persistence+and+lactose+intolerance.">Genetics of lactase persistence and lactose intolerance.</a> Annual Review of Genetics. 37, 197-219 (2003).</li><li>Enattah, N. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Independent+introduction+of+two+lactase-persistence+alleles+into+human+populations+reflects+different+history+of+adaptation+to+milk+culture.">Independent introduction of two lactase-persistence alleles into human populations reflects different history of adaptation to milk culture.</a> American Journal of Human Genetics. 82, 57-72 (2008).</li><li>Lowe, G. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+rapid+detection+of+lactose+fermentation+in+paracolon+organisms+by+the+demonstration+of+beta-D-galactosidase.">The rapid detection of lactose fermentation in paracolon organisms by the demonstration of beta-D-galactosidase.</a> Journal of Medical Laboratory Technology. 19, 21-25 (1962).</li><li>Russo, S. F., Moothart, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetic+study+of+the+Enzyme+Lactase.">Kinetic study of the Enzyme Lactase.</a> Journal of Chemical Education. 63, 242 (1986).</li></ol>

The authors have no conflicts of interest to disclose.

A detailed knowledge and understanding of enzymes, enzymatic reactions and enzyme kinetics is required for a wide range of topics spanning biology, biomedicine and pharmacology. The protocol described above uses lactase as an example of an enzyme relevant to human health for demonstrating enzymatic reactions, providing key skills that can be used in more advanced laboratory-based experiments.
This protocol has been deliberately designed to be as robust as possible, allowing students with little or no wet laboratory&#160;experience&#160;to produce interpretable results in a short space of time. In the 2014/2015 academic year at the University of Reading School of Pharmacy, a total of 144 students, organized into groups of 3, carried out the &#34;measuring lactase&#34; experiment, with all groups able to detect some level of enzymatic activity from lactase tablet extracts.
There are a number of critical steps in this protocol. First, it is essential that the initial extraction is efficient, allowing solubilization of enough active enzyme for subsequent analyses. In our experience, first year undergraduates can achieve this by following the protocol as outlined; however some guidance from laboratory demonstrators was required at this point. Although it would seem a self-evident point, a key factor in the success of this protocol is the ability to carefully measure volumes, correctly label tubes and follow instructions. While a certain level of proficiency can be assumed for many students, careful monitoring and a clear request for students to ask for assistance in the event that they are unsure of what to do next provides the greatest likelihood of a successful assay.
Student evaluation can be carried out by the in-class worksheet (available as supplemental material), asking students to note data from the experiments, comment on their results and link to background information/reading from lecture material, or by more detailed, out of class assessment with model data provided allowing for kinetic analyses to be attempted and evaluated.
The protocol presented herein is a simple example of a lactase activity assay under teaching laboratory conditions, and there is ample opportunity to increase the complexity of the experiment to allow more advanced analyses. In particular, the presented protocol provides an introduction to the concept of enzyme kinetics but does not allow for kinetic analysis of experimental data. As such, we would recommend viewing the described protocol as an initial template for classes, with the precise details adapted to suit the specific aims and talents of the student cohort undertaking the experiments. Examples of extended experiments could include: repeated measurements at different temperatures, using different substrate concentrations to allow statistical analysis, kinetic analysis of data (suitable for biochemistry students/majors), starting with several different tablets and allowing the students to evaluate different activity of enzyme in each (with the addition of control tablets, suitable for forensic science students/majors), assessing the impact of heat denaturation, or carrying out competition experiments by addition of lactose or inhibitors of lactase (Table 1). A detailed protocol for kinetic analysis of lactase has previously been published12.
An important strength of this protocol is that it combines a basic introduction to enzymology and enzyme kinetics with a real-life case study of enzymology in medicine. This makes this laboratory experiment of particular relevance to students of medicine, pharmacy, biomedical sciences and related subjects. Importantly, the fact that there is both a serious medical condition and a more widespread dietary issue associated with lactose catabolism provides the opportunity to raise a wide range of medical and ethical issues with the students. This could include the issues surrounding genetic testing for medical conditions, and associated discussions relating to gene therapy and genetic counselling, as well as the use and sale of medicinal supplements. One major limitation is that the protocol does not allow for precise estimation of enzyme concentration, due to the starting material used for the extraction. A modification to account for this, however, would be to use reagent grade enzyme for the assay. Importantly, this would also allow for more precise calculation of kinetics for the lactase enzyme.
In conclusion, assaying the activity of lactase in a teaching lab environment provides a robust, engaging and interesting introduction to the field of enzyme biology for early stage university students.

Enzymes are a specialized type of protein that act as biological catalysts for chemical reactions in living organisms1. The action of enzymes is critical for life, providing energy, disposing of waste and allowing organisms to function. Understanding enzymes is, therefore, critical for a full understanding of life. Such knowledge is essential for a wide variety of university level degree programs, ranging from the medical sciences to biology. While a detailed background ranging from principles of catalysis to theoretical models of enzyme activity can be provided to students using lectures and reading material, the properties of enzyme reactions are best comprehended by hands on practical experience of enzymes in action as previously demonstrated2. This protocol provides a simple to follow experimental paradigm for measuring enzyme activity under laboratory conditions, using lactase as an example of an enzyme with an activity relevant to human nutrition and health.
The glycosidic hydrolase lactase (EC 3.2.1.23/26) is an enzyme of central nutritional importance for mammals3. The activity of lactase is highly conserved through evolution, and derives from the beta-galactosidase family of enzymes &#8212; a family present from Escherichia coli through to Homo sapiens (Figure 1, PDB 1JZ8)4. The critical importance of lactase in a human nutritional setting stems from its role in allowing the breakdown of lactose into its constituent monosaccharide components, which can then be used to generate energy in the body. Lactase catalyzes the hydrolysis of the glycosidic bond in the disaccharide lactose, releasing galactose and glucose (Figure 2)5. These monosaccharides are then used primarily for the generation of adenosine triphosphate (ATP) via the citric acid cycle and oxidative phosphorylation6. During neonate and infant development, lactase is highly expressed in the human digestive system, breaking down lactose received from breast milk of which lactose is the primary carbohydrate component, and one of the key sources of nutrition during early years7. The medical importance of lactase is highlighted by congenital lactase deficiency (CLD), a rare autosomal recessive condition caused by mutations in the lactase gene (LCT) coding for the lactase enzyme8. New-born babies with CLD exhibit very little lactase activity, thus they cannot be fed on breast milk, any other type of milk, or formula containing lactose.
During childhood, lactase expression is normally reduced; however, this reduction following weaning varies geographically, with approximately 35% of adults worldwide continuing to express the enzyme9. Sustained expression of lactase, known as lactase persistence, allows individuals to continue to digest milk and dairy products from a range of sources. Conversely, the loss of lactase expression can lead to lactose intolerance, also known as adult-type hypolactasia (ATH), resulting from an inability to break down lactose in the gut. ATH is characterized by a build up of lactose in the colon following ingestion of lactose containing food products. In the colon, the accumulated lactose is fermented by gut microbial fauna, releasing gasses including hydrogen, methane, and carbon dioxide. The production of these gases in individuals with lactase enzyme deficiencies promote abdominal bloating, increased flatulence, pain, nausea, and borborygmi (stomach rumbling)7. Increased levels of lactose in the digestive tract can also lead to loose stools.
The control of LCT gene expression is modulated by polymorphisms located in introns of the nearby MCM6 gene. Individuals with sustained expression of lactase carry polymorphisms that function as strong distal enhancers for LCT gene expression, thus compensating the normal down regulation of LCT transcription during weaning, and consequently sustaining lactase expression in adulthood3. Enhancer polymorphisms have been suggested to have been positively selected following the domestication of cattle and camels in the Middle East over five thousand years ago9,10.
The symptoms resulting from ATH can be managed by reducing lactose intake, for example by removing dairy products from the diet. An alternative approach for ATH, and the approach of choice for CLD, is the use of lactase supplements, widely available from pharmacies. These supplements provide lactase isolated from a variety of sources, including yeast and bacteria, in a liquid or pill-based form that can be taken with or added to lactose containing food. The supplement will hydrolyze a proportion of the lactose present in the food to glucose and galactose products, thus permitting their absorption and preventing accumulation of undigested lactose substrate in the gut.
Based upon the use of lactase supplements as a dietary aid, we have developed a simple enzymology laboratory experiment suitable for first year biomedical science or pharmacy students. This laboratory experiment takes advantage of commercially available lactase supplements, and uses ortho-nitrophenol-beta-D-galactopyranoside (ONPG) to provide a colorimetric end point for measuring cleavage of glycosidic bonds by lactase (Figure 3)11. ONPG acts an artificial substrate for lactase, which when subjected to hydrolysis by this enzyme produces D-galactose and ortho-nitrophenol. The latter product has a yellow color, absorbing light at a wavelength of 420 nm. By quantifying any changes in absorbance at 420 nm following the exposure of ONPG to lactase, it is possible to estimate the activity of this enzyme. This laboratory experiment provides a demonstration of enzymatic hydrolase activity. By building in additional replicates and carrying out assays in different conditions, it is possible to incorporate more sophisticated analyses of enzyme kinetics, providing a valuable real-life example of enzymes in action relevant to human health.

<table border="0" cellpadding="0" cellspacing="0" style="width:796px;" width="797">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Lactase tablet</td>
			<td style="width:71px;">Lamberts</td>
			<td style="width:119px;">8511-60</td>
			<td style="width:392px;"></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:215px;">Phosphate buffered saline (powdered)</td>
			<td style="width:71px;">Sigma</td>
			<td style="width:119px;">P3813</td>
			<td style="width:392px;">Dissolved in deionized water to a final concentration of 100 mM</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">ONPG</td>
			<td style="width:71px;">Sigma</td>
			<td style="width:119px;">N1127</td>
			<td style="width:392px;">Dissolved in deionized water to a final concentration of 5 mM</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Sodium Carbonate</td>
			<td style="width:71px;">Sigma</td>
			<td style="width:119px;">451614</td>
			<td style="width:392px;">Dissolved in deionized water to a final concentration of 1 M</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">De-ionized water</td>
			<td style="width:71px;">NA</td>
			<td style="width:119px;">NA</td>
			<td style="width:392px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:215px;">Pestle and mortar</td>
			<td style="width:71px;">VWR</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:215px;">Spectrophotometer</td>
			<td style="width:71px;">Jenway 6315</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:215px;">Pipettes</td>
			<td style="width:71px;">Gilson</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:215px;">15 mL tubes</td>
			<td style="width:71px;">VWR</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:215px;">1.5 mL tubes</td>
			<td style="width:71px;">Eppendorf</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:215px;">Spectrophotometer cuvettes</td>
			<td style="width:71px;">Jenway</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:215px;">Vortex</td>
			<td style="width:71px;">Vortex genie 2</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:215px;">Centrifuge</td>
			<td style="width:71px;">Beckman</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:215px;">Ice bucket</td>
			<td style="width:71px;">VWR</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:215px;">Water bath</td>
			<td style="width:71px;">Thermo-Scientific</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:215px;">Weighing scales</td>
			<td style="width:71px;">Thermo-Scientific</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

measuring lactase enzymatic activity in the teaching lab

Understanding how enzymes work, and relating this to real life examples, is critical to a wide range of undergraduate degrees in the biological and biomedical sciences. This easy to follow protocol was developed for first year undergraduate pharmacy students and provides an entry-level introduction to enzyme reactions and analytical procedures for enzyme analysis. The enzyme of choice is lactase, as this represents an example of a commercially available enzyme relevant to human disease/pharmaceutical practice. Lactase is extracted from dietary supplement tablets, and assessed using a colorimetric assay based upon hydrolysis of an artificial substrate for lactase (ortho-nitrophenol-beta-D-galactopyranoside, ONPG). Release of ortho-nitrophenol following the hydrolytic cleavage of ONPG by lactase is measured by a change in absorbance at 420 nm, and the effect of the temperature on the enzymatic reaction is evaluated by carrying out the reaction on ice, at room temperature and at 37 &#176;C. More advanced analysis can be implemented using this protocol by assessing the enzyme activity under different conditions and using different reagents.

Representative results for Section 2 of the protocol are shown in Figure 4A. The control reaction, in the absence of lactase enzyme, remains clear whilst the reaction solution, containing extract from the lactase tablet, turns yellow as ONPG is hydrolyzed releasing ortho-nitrophenol. Figure 4B shows quantification using arbitrary units from Section 4 of the protocol, following analysis of samples using the spectrophotometer. Production of ortho-nitrophenol is lowest when the reaction is incubated on ice, and highest when the reaction is carried out at 37 &#176;C.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/54377/54377fig1.jpg" /> 
Figure 1: E. coli beta-galactosidase. (A)&#160;Crystal structure of beta-galactosidase from Escherichia coli, showing the tetrameric structure of the active complex. (B) Allolactose (shown in red) bound to the active site of beta-galactosidase. Images generated from PDB 1JZ84. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54377/54377fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/54377/54377fig2.jpg" /> 
Figure 2: Enzymatic action of lactase. Hydrolysis of lactose by lactase to produce beta-D-galactose and beta-D-glucose. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54377/54377fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/54377/54377fig3.jpg" /> 
Figure 3:&#160;Hydrolysis of ortho-nitrophenol-beta-D-galactopyranoside. ONPG hydrolysis by lactase to produce beta-D-galactose and ortho-nitrophenol (which is yellow in color), allowing estimation of lactase activity by measurement of absorbance at 420 nm. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54377/54377fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/54377/54377fig4.jpg" /> 
Figure 4: ONPG hydrolysis. Representative results of ONPG hydrolysis, showing control and reaction tubes (A) and representative data from Section 4 of the protocol recorded on in-class worksheets, showing raw absorbance in arbitrary units at 420 nm, corrected for background and at three different temperatures (B). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54377/54377fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Experimental Condition</td>
			<td>Experimental variables</td>
		</tr>
		<tr>
			<td>Temperature</td>
			<td>0 &#176;C, 10 &#176;C, 20 &#176;C, 30 &#176;C, 50 &#176;C</td>
		</tr>
		<tr>
			<td>Substrate concentration</td>
			<td>0 mM, 1 mM, 5 mM ,10 mM ONPG</td>
		</tr>
		<tr>
			<td>Competitive inhibition</td>
			<td>5 mM ONPG plus 0 mM, 1 mM, 5 mM, or 10 mM lactose</td>
		</tr>
		<tr>
			<td>Time dependence</td>
			<td>0 s, 15 s, 30 s, 1 min, 5 min, 10 min, 20 min</td>
		</tr>
		<tr>
			<td>Heat denaturation</td>
			<td>Lactase extract heated to 100 &#176;C for 10 min prior to assay</td>
		</tr>
	</tbody>
</table>
Table 1: Potential extended experimental condition. Suggested extended experiments, to be carried out in triplicate, investigating specific aspects of lactase biology.
Supplemental Materials. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54377/54377_SupplementalFiles.pdf" target="_blank">Please click here to download this file.</a>

Watch this Scientific Journal Video about Measuring Lactase Enzymatic Activity in the Teaching Lab at JoVE.com

Measuring Lactase Enzymatic Activity in the Teaching Lab

The enzymatic activity of lactase is essential for the catabolic processing of the disaccharide lactose. Here, the activity of lactase found in dietary supplements is assayed using a colorimetric assay. This provides students with an experimental platform for understanding the activity of lactase and enzyme kinetics.

Understanding how enzymes work, and relating this to real life examples, is critical to a wide range of undergraduate degrees in the biological and ...

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112.8K Views.  University of Reading. The enzymatic activity of lactase is essential for the catabolic processing of the disaccharide lactose. Here, the activity of lactase found in dietary supplements is assayed using a colorimetric assay. This provides students with an experimental platform for understanding the activity of lactase and enzyme kinetics.

Video: Measuring Lactase Enzymatic Activity in the Teaching Lab

Lens Transplantation in Zebrafish and its Application in the Analysis of Eye Mutants

The lens plays an important role in the development of the optic cup[1,2]. Using the zebrafish as a model organism, questions regarding lens development can be addressed. The zebrafish is useful for genetic studies due to several advantageous characteristics, including small size, high fecundity, short lifecycle, and ease of care. Lens development occurs rapidly in zebrafish. By 72 hpf, the zebrafish lens is functionally mature [3]. Abundant genetic and molecular resources are available to support research in zebrafish. In addition, the similarity of the zebrafish eye to those of other vertebrates provides basis for its use as an excellent animal model of human defects[4-7]. Several zebrafish mutants exhibit lens abnormalities, including high levels of cell death, which in some cases leads to a complete degeneration of lens tissues [8]. To determine whether lens abnormalities are due to intrinsic causes or to defective interactions with the surrounding tissues, transplantation of a mutant lens into a wild-type eye is performed. Using fire-polished metal needles, mutant or wild-type lenses are carefully dissected from the donor animal, and transferred into the host. To distinguish wild-type and mutant tissues, a transgenic line is used as the donor. This line expresses membrane-bound GFP in all tissues, including the lens. This transplantation technique is an essential tool in the studies of zebrafish lens mutants.

Lens development involves interactions with other tissues. Several zebrafish eye mutants are characterized by an abnormally small lens size. Here we demonstrate a lens transplantation experiment to determine whether this phenotype is due to intrinsic causes or defective interactions with tissues that surround the lens.

The lens plays an important role in the development of the optic cup[1,2]. Using the zebrafish as a model organism, questions regarding lens development ...

An Assay for Measuring the Activity of Escherichia coli Inducible Lysine Decarboxyase

Escherichia coli is an enteric bacterium that is capable of growing over a wide range of pH values (pH 5 - 9)1 and, incredibly, is able to survive extreme acid stresses including passage through the mammalian stomach where the pH can fall to as low as pH 1 - 22. To enable such a broad range of acidic pH survival, E. coli possesses four different inducible amino acid decarboxylases that decarboxylate their substrate amino acids in a proton-dependent manner thus raising the internal pH. The decarboxylases include the glutamic acid decarboxylases GadA and GadB3, the arginine decarboxylase AdiA4, the lysine decarboxylase LdcI5, 6 and the ornithine decarboxylase SpeF7. All of these enzymes utilize pyridoxal-5'-phospate as a co-factor8 and function together with inner-membrane substrate-product antiporters that remove decarboxylation products to the external medium in exchange for fresh substrate2. In the case of LdcI, the lysine-cadaverine antiporter is called CadB. Recently, we determined the X-ray crystal structure of LdcI to 2.0 &#197;, and we discovered a novel small-molecule bound to LdcI the stringent response regulator guanosine 5'-diphosphate,3'-diphosphate (ppGpp) 14. The stringent response occurs when exponentially growing cells experience nutrient deprivation or one of a number of other stresses9. As a result, cells produce ppGpp which leads to a signaling cascade culminating in the shift from exponential growth to stationary phase growth10. We have demonstrated that ppGpp is a specific inhibitor of LdcI 14. Here we describe the lysine decarboxylase assay, modified from the assay developed by Phan et al.11, that we have used to determine the activity of LdcI and the effect of pppGpp/ppGpp on that activity. The LdcI decarboxylation reaction removes the &alpha;-carboxy group of L-lysine and produces carbon dioxide and the polyamine cadaverine (1,5-diaminopentane)5. L-lysine and cadaverine can be reacted with 2,4,6-trinitrobenzensulfonic acid (TNBS) at high pH to generate N,N'-bistrinitrophenylcadaverine (TNP-cadaverine) and N,N&#8242;-bistrinitrophenyllysine (TNP-lysine), respectively11. The TNP-cadaverine can be separated from the TNP-lysine as the former is soluble in organic solvents such as toluene while the latter is not (See Figure 1). The linear range of the assay was determined empirically using purified cadaverine.

An Assay for Measuring the Activity of Escherichia coli Inducible Lysine Decarboxyase

The activity of the inducible lysine decarboxylase is monitored by reacting the substrate L-lysine and the product cadaverine with 2,4,6-trinitrobenzensulfonic acid to form adducts that have differential solubility in toluene.

Escherichia coli is an enteric bacterium that is capable of growing over a wide range of pH values (pH 5 - 9)1 and, incredibly, is able to survive extreme ...

Measuring Caenorhabditis elegans Life Span in 96 Well Microtiter Plates

Lifespan is a biological process regulated by several genetic pathways. One strategy to investigate the biology of aging is to study animals that harbor mutations in components of age-regulatory pathways. If these mutations perturb the function of the age-regulatory pathway and therefore alter the lifespan of the entire organism, they provide important mechanistic insights1-3.
Another strategy to investigate the regulation of lifespan is to use small molecules to perturb age-regulatory pathways. To date, a number of molecules are known to extend lifespan in various model organisms and are used as tools to study the biology of aging4-16. The number of molecules identified thus far is small compared to the genetic "toolset" that is available to study the biology of aging.
Caenorhabditis elegans is one of the principle models used to study aging because of its excellent genetics and short lifespan of three weeks. More recently, C.elegans has emerged as a model organism for phenotype based drug screens5,7,16-20 because of its small size and its ability to grow in microtiter plates.
Here we present an assay to measure C.elegans lifespan in 96 well microtiter plates. The assay was developed and successfully used to screen large libraries for molecules that extend C.elegans lifespan7. The reliability of the assay was evaluated in multiple tests: first, by measuring the lifespan of wild type animals grown at different temperatures; second, by measuring the lifespan of mutants with altered lifespans; third, by measuring changes in lifespan in response to different concentrations of the antidepressant Mirtazepine. Mirtazepine has previously been shown to extend lifespan in C.elegans7. The results of these tests show that the assay is able to replicate previous findings from other assays and is quantitative. The microtiter format also makes this lifespan assay compatible with automated liquid handling systems and allows integration into automated platforms.

Measuring Caenorhabditis elegans Life Span in 96 Well Microtiter Plates

In this protocol we present a method to measure Caenorhabditis elegans lifespan in 96 well microtiter plates.

Lifespan is a biological process regulated by several genetic pathways. One strategy to investigate the biology of aging is to study animals that harbor ...

Measuring the Osmotic Water Permeability Coefficient (Pf) of Spherical Cells: Isolated Plant Protoplasts as an Example

Studying AQP regulation mechanisms is crucial for the understanding of water relations at both the cellular and the whole plant levels. Presented here is a simple and very efficient method for the determination of the osmotic water permeability coefficient (Pf) in plant protoplasts, applicable in principle also to other spherical cells such as frog oocytes. The first step of the assay is the isolation of protoplasts from the plant tissue of interest by enzymatic digestion into a chamber with an appropriate isotonic solution. The second step consists of an osmotic challenge assay: protoplasts immobilized on the bottom of the chamber are submitted to a constant perfusion starting with an isotonic solution and followed by a hypotonic solution. The cell swelling is video recorded. In the third step, the images are processed offline to yield volume changes, and the time course of the volume changes is correlated with the time course of the change in osmolarity of the chamber perfusion medium, using a curve fitting procedure written in Matlab (the &#8216;PfFit&#8217;), to yield Pf.

Measuring the Osmotic Water Permeability Coefficient Pf of Spherical Cells: Isolated Plant Protoplasts as an Example

Measuring the osmotic water permeability coefficient (Pf) of cells can help understand the regulatory mechanisms of aquaporins (AQPs). Pf determination in spherical plant cell protoplasts presented here involves protoplasts isolation and numerical analysis of their initial rate of volume change as a result of an osmotic challenge during constant bath perfusion.

Studying AQP regulation mechanisms is crucial for the understanding of water relations at both the cellular and the whole plant levels. Presented here is ...

An Experimental and Bioinformatics Protocol for RNA-seq Analyses of Photoperiodic Diapause in the Asian Tiger Mosquito, Aedes albopictus

Photoperiodic diapause is an important adaptation that allows individuals to escape harsh seasonal environments via a series of physiological changes, most notably developmental arrest and reduced metabolism. Global gene expression profiling via RNA-Seq can provide important insights into the transcriptional mechanisms of photoperiodic diapause. The Asian tiger mosquito, Aedes albopictus, is an outstanding organism for studying the transcriptional bases of diapause due to its ease of rearing, easily induced diapause, and the genomic resources available. This manuscript presents a general experimental workflow for identifying diapause-induced transcriptional differences in A. albopictus. Rearing techniques, conditions necessary to induce diapause and non-diapause development, methods to estimate percent diapause in a population, and RNA extraction and integrity assessment for mosquitoes are documented. A workflow to process RNA-Seq data from Illumina sequencers culminates in a list of differentially expressed genes. The representative results demonstrate that this protocol can be used to effectively identify genes differentially regulated at the transcriptional level in A. albopictus due to photoperiodic differences. With modest adjustments, this workflow can be readily adapted to study the transcriptional bases of diapause or other important life history traits in other mosquitoes.

An Experimental and Bioinformatics Protocol for RNA-seq Analyses of Photoperiodic Diapause in the Asian Tiger Mosquito, Aedes albopictus

RNA-Seq analyses are becoming increasingly important for identifying the molecular underpinnings of adaptive traits in non-model organisms. Here, a protocol to identify differentially expressed genes between diapause and non-diapause Aedes albopictus mosquitoes is described, from mosquito rearing, to RNA sequencing and bioinformatics analyses of RNA-Seq data.

Photoperiodic diapause is an important adaptation that allows individuals to escape harsh seasonal environments via a series of physiological changes, ...

Measuring Glutathione-induced Feeding Response in Hydra

Hydra is among the most primitive organisms possessing a nervous system and chemosensation for detecting reduced glutathione (GSH) for capturing the prey. The movement of prey organisms causes mechanosensory discharge of the stinging cells called nematocysts from hydra, which are inserted into the prey. The feeding response in hydra, which includes curling of the tentacles to bring the prey towards the mouth, opening of the mouth and consequent engulfing of the prey, is triggered by GSH present in the fluid released from the injured prey. To be able to identify the molecular mechanism of the feeding response in hydra which is unknown to date, it is necessary to establish an assay to measure the feeding response. Here, we describe a simple method for the quantitation of the feeding response in which the distance between the apical end of the tentacle and mouth of hydra is measured and the ratio of such distance before and after the addition of GSH is determined. The ratio, called the relative tentacle spread, was found to give a measure of the feeding response. This assay was validated using a starvation model in which starved hydra show an enhanced feeding response in comparison with daily fed hydra.

Here we describe a simple assay for the quantification of the feeding response in hydra induced by the reduced form of glutathione. This assay relies on measuring the distance between the apical end of the tentacle and mouth of hydra.

Hydra is among the most primitive organisms possessing a nervous system and chemosensation for detecting reduced glutathione (GSH) for capturing the prey. ...

Measurement of Larval Activity in the Drosophila Activity Monitor

Drosophila larvae are used in many behavioral studies, yet a simple device for measuring basic parameters of larval activity has not been available. This protocol repurposes an instrument often used to measure adult activity, the TriKinetics Drosophila activity monitor (MB5 Multi-Beam Activity Monitor) to study larval activity. The instrument can monitor the movements of animals in 16 individual 8 cm glass assay tubes, using 17 infrared detection beams per tube. Logging software automatically saves data to a computer, recording parameters such as number of moves, times sensors were triggered, and animals&#8217; positions within the tubes. The data can then be analyzed to represent overall locomotion and/or position preference as well as other measurements. All data are easily accessible and compatible with basic graphing and data manipulation software. This protocol will discuss how to use the apparatus, how to operate the software and how to run a larval activity assay from start to finish.

Measurement of Larval Activity in the Drosophila Activity Monitor

This report describes a method for measuring Drosophila larval activity using the TriKinetics Drosophila Activity Monitor. The device employs infrared beams to detect movements of up to 16 individual animals. Data can be analyzed to represent motion parameters including rates and the positions of the animals within the assay chambers.

Drosophila larvae are used in many behavioral studies, yet a simple device for measuring basic parameters of larval activity has not been available. This ...

Method for Measuring the Activity of Deubiquitinating Enzymes in Cell Lines and Tissue Samples

The ubiquitin-proteasome system has recently been implicated in various pathologies including neurodegenerative diseases and cancer. In light of this, techniques for studying the regulatory mechanism of this system are essential to elucidating the cellular and molecular processes of the aforementioned diseases. The use of hemagglutinin derived ubiquitin probes outlined in this paper serves as a valuable tool for the study of this system. This paper details a method that enables the user to perform assays that give a direct visualization of deubiquitinating enzyme activity. Deubiquitinating enzymes control proteasomal degradation and share functional homology at their active sites, which allows the user to investigate the activity of multiple enzymes in one assay. Lysates are obtained through gentle mechanical cell disruption and incubated with active site directed probes. Functional enzymes are tagged with the probes while inactive enzymes remain unbound. By running this assay, the user obtains information on both the activity and potential expression of multiple deubiquitinating enzymes in a fast and easy manner. The current method is significantly more efficient than using individual antibodies for the predicted one hundred deubiquitinating enzymes in the human cell.

The current protocol details a method for measuring the activity of functionally homologous deubiquitinating enzymes. Specialized probes covalently modify the enzyme and allow for detection. This method holds the potential to identify new therapeutic targets.

The ubiquitin-proteasome system has recently been implicated in various pathologies including neurodegenerative diseases and cancer. In light of this, ...

Measuring Pressure Volume Loops in the Mouse

Understanding the causes and progression of heart disease presents a significant challenge to the biomedical community. The genetic flexibility of the mouse provides great potential to explore cardiac function at the molecular level. The mouse&#39;s small size does present some challenges in regards to performing detailed cardiac phenotyping. Miniaturization and other advancements in technology have made many methods of cardiac assessment possible in the mouse. Of these, the simultaneous collection of pressure and volume data provides a detailed picture of cardiac function that is not available through any other modality. Here a detailed procedure for the collection of pressure-volume loop data is described. Included is a discussion of the principles underlying the measurements and the potential sources of error. Anesthetic management and surgical approaches are discussed in great detail as they are both critical to obtaining high quality hemodynamic measurements. The principles of hemodynamic protocol development and relevant aspects of data analysis are also addressed.

This manuscript describes a detailed protocol for the collection of pressure-volume data from the mouse.

Understanding the causes and progression of heart disease presents a significant challenge to the biomedical community. The genetic flexibility of the ...

Measuring In Vitro ATPase Activity for Enzymatic Characterization

Adenosine triphosphate-hydrolyzing enzymes, or ATPases, play a critical role in a diverse array of cellular functions. These dynamic proteins can generate energy for mechanical work, such as protein trafficking and degradation, solute transport, and cellular movements. The protocol described here is a basic assay for measuring the in vitro activity of purified ATPases for functional characterization. Proteins hydrolyze ATP in a reaction that results in inorganic phosphate release, and the amount of phosphate liberated is then quantitated using a colorimetric assay. This highly adaptable protocol can be adjusted to measure ATPase activity in kinetic or endpoint assays. A representative protocol is provided here based on the activity and requirements of EpsE, the AAA+ ATPase involved in Type II Secretion in the bacterium Vibrio cholerae. The amount of purified protein needed to measure activity, length of the assay and the timing and number of sampling intervals, buffer and salt composition, temperature, co-factors, stimulants (if any), etc. may vary from those described here, and thus some optimization may be necessary. This protocol provides a basic framework for characterizing ATPases and can be performed quickly and easily adjusted as necessary.

Measuring In Vitro ATPase Activity for Enzymatic Characterization

We describe a basic protocol for quantitating in vitro ATPase activity. This protocol can be optimized based on the level of activity and requirements for a given purified ATPase.

Adenosine triphosphate-hydrolyzing enzymes, or ATPases, play a critical role in a diverse array of cellular functions. These dynamic proteins can generate ...