| Assay Method Information | |
| | Enzyme Kinetic Assay |
| Description: | To determine the inhibition selectivity for inhibitor candidates, human TNAP, PLAP or IAP were added to microtiter plates followed by addition of the substrate pNPP (0.5 mM) and activity was measured in 1 M DEA-HCl buffer, pH 9.8 or in 1 M Tris-HCl buffer, pH 7.5, containing 1 mM MgCl2 and 20 μM ZnCl2, in the presence of potential inhibitors (0-30 μM). TNAP, PLAP and IAP activities were adjusted to an approximate λA405 nm, equivalent to 1, measured after 30 min. Residual AP activity in the presence of inhibitors was expressed as percentage of the control activity. To investigate the mechanism of inhibition, double reciprocal plots of enzyme activity (expressed as mA405 nm min−1) vs. substrate concentration were constructed, in the presence of various concentrations of added inhibitors (0-30 μM). The y-axis intercepts of the 1/v vs. 1/[S] plots, were then plotted vs. [I] to graphically extract Ki values as the x-intercept in this plot. The numerical values from y- and x-intercepts were derived via linear regression analysis, using software Prism 3.02 (GraphPad Software, CA). These analyses were performed, using pNPP as a substrate in 1 M DEA-HCl buffer, pH 9.8, as well as in 1 M Tris-HCl buffer, pH 7.5, to determine Ki at optimal and physiological pH respectively. Inhibitors were further tested and sorted based on their kinetic properties at pH 7.4 using PPi, the relevant natural substrate of TNAP. In this part of the study, pyrophosphate sodium salt (99% ACS reagent, Sigma-Aldrich, St Louis, Mo.) was used as a substrate. Amounts of released phosphate were measured using the Biomol Green Reagent (Biomol Research Laboratories, Inc., Plymouth Meeting, Pa.). Finally, to document the potency of selected inhibitors in physiological media, TNAP inhibition by compounds of Formula I-IV (0-30 μM) was studied at pH 7.4, during catalysis of 0.1 mM pNPP, in the presence of increasing concentrations of Na2HPO4 (0-10 mM) and pyrophosphate (0-40 mM). |
| Affinity data for this assay | |
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