Competitive Inhibition occurs when the binding of the inhibitor to the active site on the enzyme prevents the binding of the substrate and vice versa. The binding of competitive inhibitors to enzymes are reversible. Non-competitive inhibition occurs when the inhibitor binds to the enzyme at a site away from the active site such that even on binding of the substrate, the enzyme functions less effectively. This type of inhibition is reversible and cannot be overcome by adding a large amount of substrate. Related Theory Enzyme inhibitors prevent the formation of an enzyme-substrate complex and hence prevent the formation of product. Inhibition of enzymes may be either reversible or irreversible depending on the specific effect of the inhibitor being used. Competitive inhibition involves a molecule, other than the substrate, binding to the enzyme's active site. The molecule (inhibitor) is structurally and chemically similar to the substrate and hence able to bind to the active site. The competitive inhibitor blocks the active site and thus prevents substrate binding. As the inhibitor is in competition with the substrate, its effects can be reduced by increasing substrate concentration. Non-competitive inhibition involves a molecule binding to a site other than the active site (an allosteric site). (Ref. to Fig. 27.3) 