Studies on ali-esterases and other lipid-hydrolysing enzymes. 3. Inhibition of the esterases of pancreas

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Abstract
Fresh rat-pan-creas suspensions contain at least 3 enzymes with esterase activity which can readily be distinguished by their sensitivity to organophos-phorus inhibitors. All 3 enzymes differ markedly from the A-esterases and ali-esterases of serum, liver and other tissues. One of these enzymes, the lipase, hydrolyzes olive oil and tributyrin rapidly, has very little activity towards triacetin and phenyl esters and is relatively in-sensitive to inhibition by most of the organophosphorus derivatives. It is, however, progressively and irreversibly inhibited by diethyl p-nitrophenyl phosphate. One of the esterases in pancreas hydrolyzes phenyl acetate, phenyl propionate and phenyl butyrate, but exhibits little or no activity towards the triglycerides. This enzyme is readily inhibited by the organophosphorus derivatives and other esterase inhibitors. Since the cholesterol esterase of pancreas is also inhibited by the organophosphorus derivatives in low concentrations, it is possible that the esterase in question may be a cholesterol esterase. Unlike the ali-esterases of serum and liver, neither of these enzymes can be inhibited in vivo by subtoxic doses of tri-o-cresyl phosphate. A 2d esterase in pancreas hydrolyzes salicyl esters, exhibits little or no activity towards the triglycerides and phenyl esters, and is insensitive to all of the organophosphorus inhibitors tested. This esterase may be a proteo-lytic enzyme.