Fig. 1.

A schematic representation of allosterism. The orthosteric sites are the sites for binding of the substrates or competitive inhibitors of enzymes and agonists or competitive antagonists of receptors. Allosteric sites are away from these sites but their binding to the protein can change its conformation. Binding of positive allosteric modulators leads to either an increase in the affinity of the substrates/agonists or it speeds up the subsequent actions. Negative allosteric modulators act as inhibitors by either altering the affinities at the orthosteric sites or by preventing changes in the protein conformation needed for the subsequent steps.