We thank Dr. Dean Brown for providing compounds from the AstraZeneca fragment library and Dr. David Parkin for providing the AGNH and UNH enzymes. Research reported in this publication was supported by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health under Award Number R15AI128585 to B. J. S. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.Research was also supported by a Horace G. McDonell Summer Research Fellowship awarded to S. N. M., a Landesberg Family Fellowship awarded to J. A. G., and Faculty Development Grants and Frederick Bettelheim Research Award from Adelphi University to B. J. S.

1. Initial test compound assays at 500 &#956;M and 250 &#956;M
<ol>
	<li>Prepare substrate and test compound for reactions.
	<ol>
		<li>Prepare stock solutions of substrate (adenosine or 5-fluorouridine) in water and 50 mM test compound in deuterated dimethyl sulfoxide (DMSO). Refer to the introduction section for concentrations of substrate solution to use.</li>
		<li>Add 12 &#956;L of substrate (adenosine or 5-fluorouridine ) to each of four 1.5 mL microfuge tubes, 1&#8211;4.</li>
		<li>Add 6 &#956;L of deuterated DM...

<ol>
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A., 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=Identification+of+proton-pump+inhibitor+drugs+that+inhibit+Trichomonas+vaginalis+uridine+nucleoside+ribohydrolase.">Identification of proton-pump inhibitor drugs that inhibit Trichomonas vaginalis uridine nucleoside ribohydrolase.</a> Bioorganic &amp; Medicinal Chemistry Letters. 24, 1080-1084 (2014).</li><li>Beck, S., Muellers, S. N., Benzie, A. L., Parkin, D. W., Stockman, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adenosine/guanosine+preferring+nucleoside+ribohydrolase+is+a+distinct,+druggable+antitrichomonal+target.">Adenosine/guanosine preferring nucleoside ribohydrolase is a distinct, druggable antitrichomonal target.</a> Bioorganic &amp; Medicinal Chemistry Letters. 25, 5036-5039 (2015).</li><li>Muellers, S. N., 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=Ligand-efficient+inhibitors+of+Trichomonas+vaginalis+adenosine/guanosine+preferring+nucleoside+ribohydrolase.">Ligand-efficient inhibitors of Trichomonas vaginalis adenosine/guanosine preferring nucleoside ribohydrolase.</a> ACS Infectious Diseases. 5, 345-352 (2019).</li><li>Veronesi, M., 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=Fluorine+nuclear+magnetic+resonance-based+assay+in+living+mammalian+cells.">Fluorine nuclear magnetic resonance-based assay in living mammalian cells.</a> Analytical Biochemistry. 495, 52-59 (2016).</li><li>Holzgrabe, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+NMR+spectroscopy+in+pharmaceutical+applications.">Quantitative NMR spectroscopy in pharmaceutical applications.</a> Progress in NMR Spectroscopy. 57, 229-240 (2010).</li><li>Bharti, S. K., Roy, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+1H+NMR+spectroscopy.">Quantitative 1H NMR spectroscopy.</a> Trends in Analytical Chemistry. 35, 5-26 (2012).</li><li>Dalvit, C., 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=Sensitivity+improvement+in+19F+NMR-based+screening+experiments:+Theoretical+considerations+and+experimental+applications.">Sensitivity improvement in 19F NMR-based screening experiments: Theoretical considerations and experimental applications.</a> Journal of the American Chemical Society. 127, 13380-13385 (2005).</li><li>Lambruschini, C., 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=Development+of+fragment-based+n-FABS+NMR+screening+applied+to+the+membrane+enzyme+FAAH.">Development of fragment-based n-FABS NMR screening applied to the membrane enzyme FAAH.</a> ChemBioChem. 14, 1611-1619 (2013).</li><li>Stockman, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=2-Fluoro-ATP+as+a+versatile+tool+for+19F+NMR-based+activity+screening.">2-Fluoro-ATP as a versatile tool for 19F NMR-based activity screening.</a> Journal of the American Chemical Society. 130, 5870-5871 (2008).</li><li>Aldrich, C., 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=The+ecstasy+and+agony+of+assay+interference+compounds.">The ecstasy and agony of assay interference compounds.</a> ACS Central Science. 3, 143-147 (2017).</li><li>Feng, B. Y., Shoichet, B. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+detergent-based+assay+for+the+detection+of+promiscuous+inhibitors.">A detergent-based assay for the detection of promiscuous inhibitors.</a> Nature Protocols. 1, 550-553 (2006).</li><li>Copeland, R. A., Basavapathruni, A., Moyer, M., Scott, M. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impact+of+enzyme+concentration+and+residence+time+on+apparent+activity+recovery+in+jump+dilution+analysis.">Impact of enzyme concentration and residence time on apparent activity recovery in jump dilution analysis.</a> Analytical Biochemistry. , 206-210 (2011).</li><li>Griveta, J. -. P., Delort, A. -. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=NMR+for+microbiology:+In+vivo+and+in+situ+applications.">NMR for microbiology: In vivo and in situ applications.</a> Progress in NMR Spectroscopy. 54, 1-53 (2009).</li><li>Nijman, S. M. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+genomics+to+uncover+drug+mechanism+of+action.">Functional genomics to uncover drug mechanism of action.</a> Nature Chemical Biology. 11, 942-948 (2015).</li></ol>

The authors have nothing to disclose.

The protocols described are generally applicable to many enzymes, provided that the substrates and/or products have resolvable signals in the NMR spectrum. However, it is critical that the concentration of substrate is close to its Km value and high enough to be detected in an NMR experiment within a reasonable timeframe. A substrate concentration no higher than 2-3x the Km value is optimal for detecting competitive, noncompetitive, and uncompetitive inhibitors4</...

Nuclear magnetic resonance (NMR) spectroscopy is well-established for characterizing and monitoring enzyme reactions1,2. Differences in chemical shifts and coupling patterns are used to distinguish substrate and product resonances, and relative resonance intensities are used to quantify the percent of reaction. Both the consumption of substrate and the creation of product are directly observed in the NMR spectrum. This contrasts with spectrophotometry or fluorescence spectroscopy, in which the reaction time course is indicated by a change in absorbance attributable to some chemical species being consumed or created. Just as with the other methods, NMR can be used to study enzyme reactions as a function of temperature, pH, or other solution conditions, and the effects of inhibitors can be determined.
More recently, NMR-based enzyme activity assays have been demonstrated for fragment screening3,4. NMR-based assays are ideally suited to work at the higher concentrations of test compounds (often as high as 1 mM) required to detect these weaker inhibitors. The dynamic range and chemical shift dispersion in the NMR experiment can easily resolve resonances from substrate, product, and test compounds. This compares favorably to spectrophotometric assays where read-out interference problems often arise from compounds with overlapping UV-vis absorption profiles. In addition, since they lack reporter enzymes, the single-enzyme NMR assays are not prone to coupled-assay false positives. This advantage makes them useful as orthogonal assays, complementing traditional high throughput screening assays and benchtop triage assays5.
In our research laboratory, NMR-based activity assays are used to identify and evaluate inhibitors of Trichomonas vaginalis nucleoside ribohydrolases. The T. vaginalis parasite causes the most prevalent non-viral sexually transmitted disease6. Increasing resistance to existing therapies7 is driving the need for novel, mechanism-based treatments, with essential nucleoside salvage pathway enzymes representing prime targets8. NMR-based activity assays have been developed for both pyrimidine- and purine-specific enzymes, uridine nucleoside ribohydrolase (UNH)9, and adenosine/guanosine preferring nucleoside ribohydrolase (AGNH)10. The reactions catalyzed by these two enzymes are shown in Figure 1. The NMR assays are being used to screen fragment libraries for chemical starting points, determine IC50 values, and weed out aggregation-based or covalent binding inhibitors11. The same assays are also being translated to assess enzyme activity in whole cells12.
Detailed protocols are provided for initial compound assays at 500 &#956;M and 250 &#956;M, dose-response assays for determining IC50 values, detergent counter screen assays, jump-dilution counter screen assays, and assays in E. coli whole cells. The protocols are generally applicable to any enzyme in which substrate and product resonances can be observed and distinguished by NMR spectroscopy. Three assumptions have been made for simplicity. First, the substrate is not specified. For NMR-based activity assays to be useful, the final concentration of substrate should be no more than 2-3x the Km value4. In the examples shown, the final concentrations of adenosine and 5-fluorouridine are 100 &#956;M (Km = 54 &#956;M) and 50 &#956;M (Km = 15 &#956;M), respectively. In the protocols, achieving these concentrations corresponds to 12 &#956;L of 5 mM adenosine or 12 &#956;L of 2.5 mM 5-fluorouridine.
Second, the amount of enzyme provided for in the protocols, 5 &#956;L, was chosen to correspond to the amount required to result in approximately 75% conversion of substrate to product in 30 min. This quantity typically represents a large dilution from a purified enzyme stock, and the dilution must be determined in advance for each enzyme. Purified AGNH and UNH enzyme stock solutions are stored at -80 &#176;C in aliquots that provide enough enzyme for several thousand reactions. Thus, the dilution factor ideally only needs to be determined or validated every few months. Third, the specific 1D NMR experiment is not specified. In the representative results, 1H NMR is shown for AGNH10 and 19F NMR is shown for UNH9, with the NMR experiment described in the corresponding references. The choice of NMR experiment depends on the enzyme reaction and substrates available as well as available NMR instrumentation. Finally, it should be pointed out that the experimental approach described does not adhere to the strict requirements of quantitative NMR (qNMR)13,14. In the protocol, a percent reaction is determined using the relative changes in intensity of the same resonance in each spectrum, rather than by determining absolute concentrations. This approach eliminates the need for data acquisition and processing modifications as well as internal or external standards, which are required for qNMR.

<table border="0" cellpadding="0" cellspacing="0" style="width:825px;" width="825">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">AGNH</td>
			<td style="width:180px;">Purified in-house</td>
			<td style="width:180px;">N/A</td>
			<td style="width:215px;">TVAG_213720</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">UNH</td>
			<td style="width:180px;">Purified in-house</td>
			<td style="width:180px;">N/A</td>
			<td>TVAG_092730</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Adenosine</td>
			<td style="width:180px;">Sigma</td>
			<td style="width:180px;">A9251</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">5-Fluorouridine</td>
			<td style="width:180px;">Sigma</td>
			<td style="width:180px;">F5130</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Dimethyl sulfoxide-D6</td>
			<td style="width:180px;">Cambridge Isotope Labs</td>
			<td style="width:180px;">DLM-10-100</td>
			<td>D, 99.9%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Potassium phosphate monobasic</td>
			<td style="width:180px;">Sigma</td>
			<td style="width:180px;">P0662</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Potassium phosphate dibasic</td>
			<td style="width:180px;">Sigma</td>
			<td style="width:180px;">P3786</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Potassium chloride</td>
			<td style="width:180px;">Sigma</td>
			<td style="width:180px;">P9541</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Deuterium oxide</td>
			<td style="width:180px;">Cambridge Isotope Labs</td>
			<td style="width:180px;">DLM-4-100</td>
			<td>D, 99.9%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Hydrochloric acid</td>
			<td style="width:180px;">Fisher Chemical</td>
			<td style="width:180px;">A144212</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Triton X-100</td>
			<td style="width:180px;">Sigma</td>
			<td style="width:180px;">X100</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:251px;">3-(Trimethylsilyl)propionic-2,2,3,3,-d4 acid sodium salt (TSP)</td>
			<td style="width:180px;">Sigma</td>
			<td style="width:180px;">269913</td>
			<td>D, 98%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">2,2,2-Trifluoroethanol-1,1-d2</td>
			<td style="width:180px;">Sigma</td>
			<td style="width:180px;">612197</td>
			<td>D, 99.5%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Pipette</td>
			<td style="width:180px;">Gilson</td>
			<td style="width:180px;">F123602</td>
			<td>PIPETMAN Classic P1000</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Pipette</td>
			<td style="width:180px;">Gilson</td>
			<td style="width:180px;">F123601</td>
			<td style="width:215px;">PIPETMAN Classic P200</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Pipette</td>
			<td style="width:180px;">Gilson</td>
			<td style="width:180px;">F123600</td>
			<td style="width:215px;">PIPETMAN Classic P20</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Microfuge tubes</td>
			<td style="width:180px;">Fisher Scientific</td>
			<td style="width:180px;">05-408-129</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Conical tubes</td>
			<td style="width:180px;">Corning</td>
			<td style="width:180px;">352099</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Microcentrifuge</td>
			<td style="width:180px;">Eppendorf</td>
			<td style="width:180px;">5418</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Vortex mixer</td>
			<td style="width:180px;">Fisher Scientific</td>
			<td style="width:180px;">02215365</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">NMR tubes</td>
			<td style="width:180px;">Norell</td>
			<td style="width:180px;">502-7</td>
			<td>Or as appropriate for the NMR</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">NMR spectrometer</td>
			<td style="width:180px;">Bruker</td>
			<td style="width:180px;">N/A</td>
			<td>AvanceIII500</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Prism software</td>
			<td style="width:180px;">GraphPad</td>
			<td style="width:180px;">N/A</td>
			<td>Version 5.04</td>
		</tr>
	</tbody>
</table>

nmr-based activity assays for determining compound inhibition, ic50 values, artifactual activity, and whole-cell activity of nucleoside ribohydrolases

NMR spectroscopy is often used for the identification and characterization of enzyme inhibitors in drug discovery, particularly in the context of fragment screening. NMR-based activity assays are ideally suited to work at the higher concentrations of test compounds required to detect these weaker inhibitors. The dynamic range and chemical shift dispersion in an NMR experiment can easily resolve resonances from substrate, product, and test compounds. This contrasts with spectrophotometric assays, in which read-out interference problems often arise from compounds with overlapping UV-vis absorption profiles. In addition, since they lack reporter enzymes, the single-enzyme NMR assays are not prone to coupled-assay false positives. This attribute makes them useful as orthogonal assays, complementing traditional high throughput screening assays and benchtop triage assays. Detailed protocols are provided for initial compound assays at 500 &#956;M and 250 &#956;M, dose-response assays for determining IC50 values, detergent counter screen assays, jump-dilution counter screen assays, and assays in E. coli whole cells. The methods are demonstrated using two nucleoside ribohydrolase enzymes. The use of 1H NMR is shown for the purine-specific enzyme, while 19F NMR is shown for the pyrimidine-specific enzyme. The protocols are generally applicable to any enzyme where substrate and product resonances can be observed and distinguished by NMR spectroscopy. To be the most useful in the context of drug discovery, the final concentration of substrate should be no more than 2-3x its Km value. The choice of NMR experiment depends on the enzyme reaction and substrates available as well as available NMR instrumentation.

Figure 2 shows the results for testing two compounds against AGNH using 1H NMR following section 1. The enzyme reaction is most easily observed and quantified by the disappearance of adenosine singlet and doublet resonances at 8.48 ppm and 6.09 ppm, respectively, and the appearance of an adenine singlet resonance at 8.33 ppm as observed in the 30 min control spectrum. In the presence of 500 &#956;M compound 1, no product is formed as evidenced by the lack of an adenine resonance a...

Watch this Scientific Journal Video about NMR-Based Activity Assays for Determining Compound Inhibition, IC50 Values, Artifactual Activity, and Whole-Cell Activity of Nucleoside Ribohydrolases at JoVE

NMR-Based Activity Assays for Determining Compound Inhibition, IC50 Values, Artifactual Activity, and Whole-Cell Activity of Nucleoside Ribohydrolases

NMR-based activity assays have been developed to identify and characterize inhibitors of two nucleoside ribohydrolase enzymes. Protocols are provided for initial compound assays at 500 &#956;M and 250 &#956;M, dose-response assays for determining IC50 values, detergent counter screen assays, jump-dilution counter screen assays, and assays in E. coli whole cells.

NMR-Based Activity Assays for Determining Compound Inhibition, IC50 Values, Artifactual Activity, and Whole-Cell Activity of Nucleoside Ribohydrolases

NMR spectroscopy is often used for the identification and characterization of enzyme inhibitors in drug discovery, particularly in the context of fragment ...

NMR-based activity assays provide an effective method for identifying, evaluating, and validating inhibitors for a given enzyme. They are particularly well-suited for fragment screening. NMR assays are amenable to the higher compound concentrations required for weaker inhibitors.In addition, the lack of reporter enzymes makes them less prone to false positives. We use the NMR assays in our lab to identify and characterize the inhibitors of two enzymes from Trichomonas vaginalis. Both enzymes represent new targets for novel anti-trichomonal drugs.The NMR assays are generally applicable to any area of research that involves enzymes, and they can even be used to study the enzymes inside cells. The most important aspects of the technique are to ensure that the correct reagent volumes are pipetted and the reaction components are thoroughly mixed. To prepare the substrate and test compounds, add 12 microliters of substrate to each of four 1.5-milliliter microfuge tubes and add six microliters of deuterated DMSO to the zero-minute control and 30-minute control tubes.Add six microliters of the test compound to the first experimental tube and three microliters of the test compound and three microliters of deuterated DMSO to the second experimental tube. Next, add 300 microliters of deuterium oxide to a 15-milliliter tube containing 2.59 milliliters of reaction buffer, followed by 25 microliters of enzyme solution. Gently invert the tube two times to mix reaction stock solution and add 10 microliters of 1.5 molar hydrochloric acid to a 1.5-milliliter tube containing 582 microliters of reaction stock solution.Then, transfer the entire volume of reaction stock solution and acid to the zero-minute control tube to simultaneously initiate and quench the zero-minute control reaction. Aspirating and dispensing the sample two times in a slow but deliberate manner. Initiate and run the remaining three reactions in staggered fashion, immediately transferring 582 microliters of the reaction stock solution to the first experimental tube and mixing the sample two times as just demonstrated.A careful aspiration and dispensing ensures a complete mixing during the initiation steps. Be consistent with each sample to ensure differential mixing is not a variable. After 30 seconds, transfer 582 microliters of reaction stock solution to the second experimental tube and mix, followed by the addition of another 582 microliters of reaction stock solution to the 30-minute control tube 30 seconds after initiating the reaction in the second experimental tube.After 30 minutes, add 10 microliters of 1.5-molar hydrochloric acid to the first experimental tube, repeating the quenching at 30-second intervals for the second experimental and 30-minute control tubes. When all of the reactions have been quenched, transfer 600 microliters of solution from each reaction to NMR tubes. To calculate the percent conversion of substrate for the control spectra, load the samples onto the spectrometer, collect the NMR spectra, and overlay the spectra for the zero and 30-minute controls.Scale the substrate signal in the zero-minute control to match the 30-minute control and note this percentage. Then, calculate the percent conversion as 100 minus the percentage from the matching of the substrate signals. To calculate the percent conversion of the substrate for the reactions containing the test compound, overlay the spectra for the zero-minute control and the first reaction containing the 500-micromolar test compound and scale the substrate signal in the zero-minute control to match the spectrum with the test compound.Note this percentage, and use it to calculate the percent conversion as just demonstrated. Then, overlay the spectra for the zero-minute control and the first reaction containing the 250-micromolar test compound, and scale the substrate signal in the zero-minute control to match the spectrum with the test compound. After noting the percentage, use it to calculate the percent conversion.To calculate the percent reaction and percent inhibition for each test compound concentration, first, calculate the percent reaction as the percent conversion of the test compound, divided by the percent conversion of the control times 100. Then calculate the percent inhibition as 100 minus the percent reaction. To perform a detergent counter screen assay, add 300 microliters of deuterium oxide and 25 microliters of enzyme solution to a 15-milliliter tube containing 2.59 milliliters of reaction buffer.Gently invert the tube two times to mix the reaction stock solution, and add two microliters of Triton X-100 detergent to 20 milliliters of reaction buffer. Then, add 2.59 milliliters of reaction buffer, containing 0.01%Triton X-100 detergent to a new 15-milliliter conical tube. Then add 300 microliters of deuterium oxide and 25 microliters of enzyme solution to the tube.Gently invert the tube two times to mix reaction stock solution. Then, determine the percent inhibition for the 100-micromolar and 50-micromolar test compounds as just demonstrated. Using the reaction stock solution without detergent, for one set of four tubes and the reaction stock solution with detergent for a second set of four tubes.To perform a jump-dilution, transfer 468 microliters of reaction buffer and 60 microliters of deuterium oxide to a tube containing 53.8 microliters of reaction buffer, five microliters of enzyme solution, and 1.2 microliters of DMSO that has been incubating for 30 minutes. Aspirate and dispense the mixture two times in a slow, but deliberate manner. Before transferring 468 microliters of reaction buffer and 60 microliters of deuterium oxide to a tube containing 53.8 microliters of reaction buffer, five microliters of enzyme solution, and 1.2 microliters of test compound that has been incubating for 30 minutes.Mix the second reaction two times as demonstrated. And immediately transfer 588 microliters of solution from the jump-dilution DMSO control tube to a tube containing 12 microliters of substrate with mixing. Continue transferring 588 microliters from the jump-dilution test compound tube, the undiluted DMSO control tube, and the undiluted test compound tube to each of three 1.5-milliliter tubes, containing 12 microliters of substrate per tube with mixing at 30-second intervals thereafter.Then wait 30 minutes before quenching the reactions, collecting the NMR spectra, and calculating the percent inhibition for each compound as just demonstrated. Here the results for testing two compounds against AgNH in an initial test compound assay using proton NMR as demonstrated are shown. The enzyme reaction is most easily observed and quantified by the disappearance of the adenosine singlet and doublet resonances at 8.48 and 6.09 parts per million respectively.And the appearance of an adenine singlet residence at 8.33 parts per million as observed in the 30-minute control spectrum. In this figure, the results for testing a compound at two concentrations against AgNH in a detergent counter-screen assay using proton NMR as demonstrated are shown. Only minimal differences are observed in the intensities of the substrate and product signals using the two conditions, indicating that the observed enzyme inhibition is not an artifact of compound aggregation.Note that resonances arising from the tested compound and the detergent do not interfere with the substrate or product resonances. The results for testing a compound in a jump-dilution assay against AGNH using proton NMR as demonstrated reveal a reduced intensity of the substrate signal in the 20-micromolar reaction compared to the 200-micromolar reaction, indicating that the inhibition is reversible. A complete sample mixing during the initiation of each reaction and for the jump-dilutions is critical.A careful and consistent aspiration and dispensing is required. NMR-based assays can also be used to measure the enzyme activity in whole cells, using a solution containing suspended cells in place of the reaction buffer and enzyme. Our anti-trichomonal drug discovery efforts continue to rely on these assays to measure the potency of newly synthesized compounds against the ribohydrolase enzymes.Even though it is used in only very small quantities, the hydrochloric acid used to quench the reactions is hazardous and should be used with the proper personal protective equipment.

nmr-based-activity-assays-for-determining-compound-inhibition-ic50

Research

JoVE Journal

Chemistry

9.8K 조회수.  Adelphi University. NMR 기반 활성 작용법은 주어진 효소에 대한 억제제의 식별, 평가 및 유효성을 검사하는 효과적인 방법을 제공합니다. 그들은 특히 단편 스크리닝에 적합합니다. NMR 아세약은 약한 억제제에 필요한 더 높은 화합물 농도에 순종한다.또한, 기자 효소의 부족은 그(것)들을 거짓 긍정에 보다 적게 수그립니다. 우리는 트리코모나스 질에서 두 효소의 억제제를 식별하고 특성화...

비디오: NMR-Based Activity Assays for Determining Compound Inhibition, IC50 Values, Artifactual Activity, and Whole-Cell Activity of Nucleoside Ribohydrolases