Ester-splitting activity of the electroplax

Abstract

1.1. The hydrolysis of acetylcholine, dl-acetyl-β-methylcholine, ethyl chloroacetate, triacetin and butyrylcholine by intact and homogenized isolated single cells and by the connective tissue between electroplax has been tested. Some connective tissue remains attached to the electroplax; a correction for this extracellular esterase was therefore applied to evaluate esterase activity of the electroplax proper.2.2. The electroplax enzyme displays the characteristics of acetylcholinesterase. The connective tissue enzyme has neither the characteristics of acetylcholinesterase, human-serum cholinesterase, aliesterase nor arylesterase. In some respects, however, it resembles the cholinesterase of certain piscine plasmas.3.3. Hydrolysis of low concentrations of acetylcholine by intact cells is mainly by acetylcholinesterase of the electroplax, whereas high concentrations of acetylcholine are mainly hydrolyzed by the connective tissue esterase. Both enzymes are inhibited by physostigmine. Ethyl chloroacetate is hydrolyzed by at least 2 enzymes in the electroplax, only one of which is inhibited by physostigmine.4.4. There is a strong permeability barrier to the penetration of acetylcholine to the interior enzyme of the intact electroplax. This barrier is less strong for dl-acetyl-β-methylcholine, ethyl chloroacetate, triacetin and butyrylcholine.5.5. Concentrations of physostigmine which block electrical activity markedly depress acetylcholine hydrolysis. Tetracaine even in much higher concentrations than required to block electrical activity only slightly inhibits acetylcholine hydrolysis. Inhibition by neostigmine is intermediate between that of tetracaine and physostigmine.