text: In mixed inhibition the inhibitor may bind to the enzyme whether or not the substrate has already bound. Hence mixed inhibition is a combination of competitive and noncompetitive inhibition. Furthermore, the affinity of the inhibitor for the free enzyme and the enzyme-substrate complex may differ. By increasing concentrations of substrate [S], this type of inhibition can be reduced (due to the competitive contribution), but not entirely overcome (due to the noncompetitive component). Although it is possible for mixed-type inhibitors to bind in the active site, this type of inhibition generally results from an allosteric effect where the inhibitor binds to a different site on an enzyme. Inhibitor binding to this allosteric site changes the conformation (that is, the tertiary structure or three-dimensional shape) of the enzyme so that the affinity of the substrate for the active site is reduced.
  These four types of inhibition can also be distinguished by the effect of increasing the substrate concentration [S] on the degree of inhibition caused by a given amount of inhibitor. For competitive inhibition the degree of inhibition is reduced by increasing [S], for noncompetitive inhibition the degree of inhibition is unchanged, and for uncompetitive (also called anticompetitive) inhibition the degree of inhibition increases with [S].