MECHANISTIC MODEL FOR BUTYRYLCHOLINESTERASE

A plausible mechanism of action of horse serum butyrylcholinesterase [EC 3.1.1.8] is proposed. It includes substrate activation at the level of deacylation. The rate constant for the acylation of the enzyme appears to be much greater than the rate constant for the deacylation, at low substrate concentrations. At higher substrate concentrations the rate constants become more similar. No interaction between the 4 subunits in binding of inhibitors or in the catalysis was observed. There is 1 esteratic and 1 anionic site/subunit apparent from labeling studies with [32P]DFP and binding studies with N-methylacridine. Although the tetrametric form of the enzyme appears to be the native one, the monomeric and several other aggregated and dissociated states are catalytically active.