Specificity and Catalytic Effectiveness of Enzymes

Enzymes, which are usually proteins, are biological catalysts--agents that change the rate of a reaction but are unchanged by the reaction. The molecules, which an enzyme reacts with, are called substrate. Enzymes reduce the activation energy needed for a reaction. An active site is the specific portion of an enzyme that attaches to the substrate by means of weak chemical bonds. Active sites can lower the activation energy of the reactants by providing suitable microenvironment, …

…bind to a part of the enzyme away from the active site and may also regulate an enzyme activity. Molecules that inhibit or activate enzyme activity may bind to an allosteric site, a receptor site separate from the active site. Allosteric enzymes may be critical regulators of metabolic pathways. Metabolic pathways are commonly regulated by feedback inhibition, in which the product of a pathway acts as an inhibitor of an enzyme early in the pathway.