Unusual catalytic activities and functions of cholinesterases.

Cholinesterases (acetylcholinesterase and butyrylcholinesterase) have been shown to exhibit not only esterase activity but also an amine sensitive aryl acylamidase and a metallo-carboxypeptidase activities. There is also evidence to indicate that they have functions in the substantia nigra of brain, in neural cell differentiation, cell division and tumorigenesis, cell-adhesion and detoxication mechanisms. Butyrylcholinesterase is suggested to act as a back-up enzyme in acetylcholinesterase knock-out mice. Cholinesterases have catalytic or non-catalytic roles in these functions. Partial sequence homology to many other proteins having different functions and a metal binding site which can influence functions are probably factors that confer the non-cholinergic functions and activities on cholinesterases.