Allosteric Enzymes

Allosteric enzymes are regulated by compounds that bind at a site distinct from the active site - called an allosteric site - and cause a reversible change in the shape of the enzyme, including its active site. This shape change in turn affects how readily the substrate can bind to the enzyme, effectively turning the enzyme's activity up or down without competing directly for the active site itself. A compound that acts this way is called an allosteric inhibitor (or, in the opposite direction, an allosteric activator). A key example is the enzyme hexokinase, which catalyses the conversion of glucose to glucose-6-phosphate as the first step of glycolysis: hexokinase is inhibited by its own reaction product, glucose-6-phosphate, binding at an allosteric site. Because the inhibitor here is the pathway's own …