[Different aspects of the substrate specificity of the cholinesterase in the optical ganglia of the Pacific Ocean squid Todarodes pacificus].

It is the first time when the substrate specificity is considered as a complex phenomenon, taking into account an influence of substrate structure on the rate of enzymatic hydrolysis and interaction of cholinesterases with reversible and irreversible inhibitors. Kinetic parameters of hydrolysis of 18 esters, including choline, ammonium and indophenol derivates, are presented, as affected by cholinesterase from optical ganglia of pacific squid Todarodes pacificus, by acetylcholinesterase from human erythrocytes and by butyrylcholinesterase from horse serum. Some peculiarities of the squid cholinesterase are revealed, which are as follows: a low specificity at a rather high hydrolytic efficiency, the sensitivity towards inhibitory effects of several substrates at high concentrations. Reversible inhibition of the squid enzyme by ammonium inhibitors was dependent on the nature of substrates to a greater extent than that of the other enzymes. The substrate structure also conditioned various aspects of "the protective effect" in the course of irreversible inhibition of the squid cholinesterase by organophosphorous inhibitors.