Structure and Function of Acetylcholinesterase

This chapter discusses the structure and function of the enzyme acetylcholinesterase (ACh-ase). The enzyme is a dimer, each protomer comprising two nonidentical chains. The nonidentity of the two groups of polypeptide chains is supported by the determination of the number of active sites of ACh-ase. The α-chain of ACh-ase contains an active site. The α and β chains together may form an active unit. Acetylcholine (Ach) is released by excitation in the excitable membranes as a specific signal and causes a conformational change of the ACh receptor, thereby releasing Ca2+ ions bound to carboxyl groups of the protein. Ca2+ ions are involved in the excitability of nerve and muscle fibers; the Ca2+ ions released induce conformational changes of phospholipids and other polyelectrolytes. Thus, these reactions act as typical amplifiers of the signal given by ACh. ACh-ase by hydrolyzing ACh permits the receptor to return to its original conformation; the barrier of the ion movements is thereby re-established.