Binding competition

Figure 7.6 Double reciprocal plot for a tight binding competitive enzyme inhibitor, demonstrating the curvature of such plots. The dashed lines represent an attempt to fit the data at lower substrate concentrations to linear equations. This highlights how double reciprocal plots for tight binding inhibitors can be misleading, especially when data are collected only over a limited range of substrate concentrations.

Figure 7.7 Plot of IC50 as a function of substrate concentration (plotted as the ratio [S]/ATM on the x-axis) for tight binding competitive (closed circles) and tight binding uncompetitive (open circles) enzyme inhibitors.

For tight binding competitive inhibition, the relationship is given by... 

From the pattern of IC50 dependence on [5] seen in a replot such as those shown in Figures 7.7 and 7.8, one can diagnose the inhibition modality and thus convert either the IC50 or the Klw value (from Equation 7.16) to a true dissociation constant by application of the appropriate equation above (e.g., as seen in Equation 7.22, the relationship between K tpp and K for a tight binding competitive inhibitor is... 

Newport In the absence of PAR-2, PAR-3 can spread uniformly and vice versa. Do you think they bind competitively to the same sites ... 

Naloxone is a pure opioid antagonist that binds competitively to opioid receptors but does not produce an analgesic response. It is used to reverse the toxic effects of agonist and agonist-antagonist opioids. 

Fig. 3.9 ALIS-MS results for the titration of 5 pM HSA with warfarin in the presence of a 5 im concentration of its stable isotope-labeled congener warfarin-De. Increasing concentrations of warfarin reduce the response of warfarin-De due to isosteric binding competition. Reprinted from [39] with permission from the American Chemical Society.

Fig. 3.10 Examples of isosteric binding competition. (A) ALIS-MS results for the titration of 5 pM Zap-70 by staurosporine in the presence of a 5 m concentration of its structural congener K252a and (B) titration of 5 pM DHFR with the known DHFR inhibitor trimethoprim in the presence of ligand NCD-157 at 5 pm concentration. Linear MS response ratios in these experiments are consistent with direct binding competition. (C) Compound structures.

Fig. 3.11 Examples of allosteric binding competition. Titration of 5 pM Akt-1 plus 5 pM staurosporine by (A) NGD-28835 and (B) Merck-1 does not yield linear response ratios for the two competing ligands. Asymptotically bound response ratios indicate allosteric binding between these two...

Fig. 3.13 The ACE50 method demonstrated for a mixture of ligands at 1 tM per component to the M2 receptor at 5 pM concentration. (A) NGD-3350 requires the greatest competitor concentration to be competed from the receptor, indicating that it is the highest affinity ligand. (B) Ratio plots indicate direct binding competition with atropine. (C) Select compound structures. Reprinted from [39] with permission from the American Chemical Society.

Figure 20. Summary of N3 /F binding competition experiments for native laccase. Continued on next page.

There are three biochemical mechanisms of CYP inhibition competitive, mechanism-based, and metabolite-intermediate-complex (Fig. 5.3). Each type of inhibitor differs in the nature of CYP binding. Competitive inhibitors are reversibly bound and can be competed off of the docking site if another substrate of higher affinity is present at a higher concentration. Therefore,... 

Mechanism of Action Acts as an IL-2 receptor antagonist by binding with high affinity to the alpha chain of the IL-2 receptor complex and inhibits IL-2 binding Competitively inhibits IL-2 mediated activation of lymphocytes... 

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