Studies on ali-esterases. 4. Differentiation of esterases in pancreas and brain by the use of organophosphorus inhibitors

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Abstract
The substrate specificities of the esterases in rat pancreas and brain were studied with organophosphorus compounds as selective esterase inhibitors. The pancrease contains at least 2 enzymes with esterase activity which are relatively resistant to inhibition by diethyl p-nitrophenyl phosphate (E600). The data suggest that the E600-re-sistant activity towards salicyl butyrate is due to carboxypeptidase or an enzyme with similar properties, whereas the E600-resistant activity towards ethyltyrosine is probably due to chymotrypsin. The enzyme in pancreas identified previously as cholesterolesterase (Fodor, 1950; Myers et al. 1955b) appears capable of hydrolyzing a variety of esters including the ethyl esters of tyrosine, phenylalanine and leucine. The low activity towards these amino acid esters probably reflects the broad substrate specificity of this enzyme. Three ali-esterases with distinct substrate-specificity patterns could be distinguished in brain homogenates. These enzymes are distinct from the cholinesterases and from the cathepsin in brain, described by Krimsky and Racker (1949). The possible physiological functions of these enzymes and the differentiation of esterases by means of selective inhibitors are discussed.