Reversible competitive inhibition

A competitive inhibitor classically has nearly structural similarities to the common substrate for the enzyme. Therefore it competes with substrate molecules to bind to the active site. The enzyme may bind either an inhibitor molecule or a substrate molecule, but not both at the similar time. It binds reversibly to the active site. In high substrate  concentrations the  action  of  a  competitive  inhibitor  is  reduce  because  a  sufficiently  high substrate  concentration  will successfully  compete  out the inhibitor  molecule  in

      Figure: Structure and mechanism of action of (a) diisopropylphosphofiuoridate  (DIPF) and (b) iodoacetamide.

Figure: The characteristics of competitive inhibition. (a) A competitive inhibitor competes with the substrate for binding at the active site of the enzyme; (b) the enzyme can bind either substrate or the competitive inhibitor but not both; (c) Lineweaver-Burk plot showing the effect of a competitive inhibitor on K_m  and V_max.

binding to the active site. Therefore there is no modification in the V_max of the enzyme but the apparent affinity of the enzyme for its substrate reduce in the presence of the competitive inhibitor, and thus K_m increases.

A well example of competitive inhibition is gives through succinate dehydrogenase. That enzyme uses succinate  as its substrate  and is competitively  inhibited through malonate  that  differs  from  succinate  in having  one rather  than two methylene  groups that is described in above figure. Several drugs work through mimicking  the structure of the substrate  of  a  goal  enzyme,  and  thus  act  as  competitive  inhibitors  of  the enzyme. The Competitive inhibition can be recognized through using a Lineweaver–Burk plot.  V₀ is measured at varient substrate concentrations in the presence of a fixed concentration of inhibitor. A competitive  inhibitor  rise  the slope  of the  line  on  the  Lineweaver–Burk plot  and  alters  the  intercept  on  the  x-axis because K_m is increased but leaves the intercept  on the y-axis not changed  (because Vmax  remains constant).