Abstract
It is well known that most of the compounds of quaternary ammonium such as choline and its derivatives, muscarine, methylene blue, oxazine-, phenazine-, acridine derivatives inhibit cholinesterases (ChE). Physiologically, ChE hydrolyzes acetylcholine which is a neurohumoral transmitter in the body and produces acetic acid and choline which are inactive substances pharmacologically. Chemically, the reaction velocity decreases during the course of hydrolysis of ACh more than expected for the first order reaction.
The inhibiting action of choline on the enzymic hydrolysis of ACh by blood serum has been first demonstrated by Roepke (1). Later Süllmann (2) stated that choline inhibited the hydrolysis of tributyrine by blood serum, but not that by red blood cells. Recently Augustingsson (3) mentioned that this falling-off of the reaction constants is due in part to the inhibiting action of choline produced during the reaction. Moreover, the competitive inhibition of choline on ChE was true in some definite cases, demonstrated in experiments with varying choline concentrations as well as varying substrate concentrations. In most cases, this inhibition was competitive, but in some cases such as tributyrine hydrolysis by the enzymes of horse plasma and of helix blood was non-competitive. Finally, he concluded that the competitive inhibition of hydrolysis of ACh by choline was caused by a shift of the optimum substrate concentration to higher concentration.
During the course of the study on the activation of ChE by chemical compounds in our department (4, 5) I have found that choline activates ChE in some cases.
