A NOTE ON THE IDENTITY OF PORCINE LIVER CARBOXYLESTERASE AND PROLYL-BETA-NAPHTHYLAMIDASE

Prolyl-beta-naphthylamidase from porcine liver is compared with the two prevalent isoenzymes of pig liver carboxylesterase by isoelectrofocusing experiments and by inhibition studies with phenyl-methyl-sulfonyl fluoride. The results suggest that prolyl-beta-naphthylamidase is identical with the amide-cleaving isoenzyme of carboxylesterase, not with the usually predominant methyl butyrate-hydrolysing isoenzyme. It is questionable whether the recently published sequence of prolyl-beta-naphthylamidase does belong to this enzyme or to the predominant carboxylesterase without amidase activity. Surprisingly, the amide-cleaving carboxylesterase isoenzymes from rat liver have almost no activity with prolyl-beta-naphthylamide.