Cholinesterase of squid optical ganglia.

Abstract

Optical ganglia of squid (Ommatostrephes sloanei‐pacificus) possess very high cholinesterase activity. Squid cholinesterase is located on the level of layers r2–r3 of plexiform zone in ganglion cortex. The activity of catalytic site of squid cholinesterase was equal to 1.2 × 105 min−1. The hydrolysis rates of acetylcholine, butyrylcholine and acetyl‐β‐methylcholine in the presence of squid cholinestarse were the same (in optimal substrate concentrations). But their Km values were different (the lowest ones for acetylcholine); squid cholinesterase did not hydrolyze benzoylcholine. All organophosphorus inhibitors studied possessed a high activity with regard to squid cholinesterase. It was shown that O‐ethyl‐S(3,3‐dimethyl‐butyl)‐methyl‐thiophosphonate (LG‐56) is a selective inhibitor of squid cholinesterase. Substrate and inhibitor specificity and catalytic activity of squid cholinesterase differed essentially from those of acetylcholinesterase and serum cholinesterase.