Describe the types of control mechanisms to which enzymes are subject.
Because enzymes are responsible for controlling so many reactions within the body, enzymes, in turn, are subject to numerous control mechanisms, including sensitivity to temperature, pH, substrate concentration, and, especially, chemical agents that can block or disable enzymes' active sites. Competitive inhibition occurs when chemical agents that resemble the substrate very closely bind with the enzyme's active site, thereby preventing the substrate from doing so. Noncompetitive inhibition occurs when chemical agents bind away from an enzyme's active site and reduce the rate at which the enzyme catalyzes the reaction. Allosteric inhibition, a special type of noncompetitive inhibition, occurs when negative modulators stabilize allosteric enzymes, or enzymes that can exist in either an active or inactive state, in their inactive state. Allosteric enzymes that have two or more identical binding sites for the same type of substrate are often subject to the enzyme-enhancing phenomenon called cooperativity, where the binding of one substrate molecule to the enzyme greatly increases the affinity of the remaining sites for the substrate.
