Enzymes may have other binding sites, called control sites, which interact with other molecules. These other molecules may improve or interfere with the enzyme's ability to recognize and bind its substrate. Coenzymes may assist the functioning of enzymes. They work with the enzyme and may serve as hydrogen or electron acceptors. They may help to position the substrate molecules in ways that facilitate the initiation of reactions.
Inhibitors interfere with enzyme function.
Competitive inhibitors are similar in shape to the enzyme's substrate and bind to the active site of the enzyme. A competitive inhibitor physically competes with the substrate for access to the enzyme. Non-competitive inhibitors bind to the control site and partially block the active site or alter the shape of the enzyme. Other inhibitors may attach to the enzyme for briefer periods of time and simply block temporarily the enzyme's activity. Many enzymes are allosteric enzymes.