A competitive inhibitor can bind reversibly to active sites of an enzyme. In this way it competes with substrate for the active site and slows down the rate of the reaction , A simple inhibition would be characterized, in the symbolism of Box 6.2, by the equation in Box 6.3, where I is the inhibitor, K" is its binding constant to the enzyme M, and K, is the dissociation constant for MIn , Inhibition can be studied by consideration of the combined effects of the schemes in Boxes 6.2 and 6.3 on the initial rate V0. If the experiment is done at constant concentration of substrate and a series of concentrations of inhibitor, the appropriate expression is where fM,0 (Table 6.1) denotes enzyme not bound to inhibitor, Vmax was defined in Section B.3, /, i is the fraction of enzyme bound to inhibitor, and Vt is the apparent maximum velocity contributed by the MI state of the enzyme (this may be negative). The regression model is given in Table 6.13.
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