Cholinesterases

Abstract

IT is known that the cholinesterases from various animal tissues are not identical, and it has been proposed that two types of acetylcholine-splitting enzymes exist. This ‘type theory' does not explain fully some of my recent observations¹. Substrate specificity depends probably on the protein character of the enzyme molecule, which may vary from tissue to tissue. In blood serum, the enzyrne is probably an albumin ; in the red blood cells, where it has been shown to be bound to the cell membrane, it is probably a lipoprotein. This is also true for the cholinesterase of the nervous system, where the enzyme is bound to the cell structure. Hence, the red-cell esterase would be expected to be related to the nerve esterase rather than the serum esterase, and this has, in fact, been demonstrated. The enzymes from brain and red cells are said to be ‘specific' cholinesterases, and in addition a ‘non-specific' cholinesterase is said to exist, for example, in human serum, whicji hydrolyses acetylcholine as well as aliphatic esters, for example, tributyrin.