STEREOSPECIFICITY IN THE ENZYMATIC HYDROLYSIS OF TABUN AND ACETYL-β-METHYLCHOLINE CHLORIDE

Abstract

The hydrolysis of the powerful cholinesterase inhibitor, tabun, at pH 7 to 7.5 by a rat serum enzyme in bicarbonate buffer involves two simultaneous first-order reactions. A fast, enzyme-catalyzed reaction destroys the toxic dextrorotatory isomer of tabun. The much slower hydrolysis of the levorotatory and apparently non-toxic isomer is probably a non-enzymatic reaction. The enzymatic hydrolysis of acetyl-dl-β-methylcholine chloride by a rat brain homogenate has been studied as a model reaction. Only one-half of the racemic compound is hydrolyzed in contrast to the complete hydrolysis of acetylcholine chloride by the same enzyme source. These results and the results of toxicity studies on the hydrolyzing solution indicate that true cholinesterase hydrolyzes only the dextrorotatory isomer of acetyl-dl-β-methylcholine chloride.