Under certain conditions, a protein may have a stable alternate conformation, or shape, that enables it to carry out a different biological function. Proteins that exhibit this characteristic are called allosteric. Allosteric proteins can change their shape and function depending on the environmental conditions in which they are found.

(Greek allos = other , stereos = solid or three-dimensional) used to describe proteins (receptors, enzymes, motors) that have at least 2 sites that alter the protein properties. The active site binds the principal substrate. The regulatory site(s) bind effector molecule(s) that influence the protein's biological activity.

Alteration of a protein conformation resulting in alteration of function (e.g. non-competitive receptor inhibition).