Abstract
An aminopeptidase, the enzyme-hydrolyzing alanine-p-nitroanilide (APAase), from leaves of Euonymus alatus f. ciliato-dentatus was purified about 1,400-fold by a combination of ion-exchange and gel filtration column chromatographies. Polyacrylamide gel electrophoresis showed the purified APAase to be homogenous. The molecular weight of this APAase was estimated to be about 100,000, and the optimum pH for its hydrolytic activity against alanine-p-nitroanilide (APA) was 8.6–9.0. APAase hydrolyzed alanine-β-naphthylamide (alanine-NA), glycine-NA, lysine-NA and arginine-NA. It was inhibited slightly by p-chloromercuribenzoate (PCMB) and iodoacetic acid and was not activated by thiol reagents. Therefore, a sulfhydryl group could not be present at the active site of APAase. APAase was inhibited strongly by 1,10-phenanthroline, but was unaffected by EDTA. Of the metal ions tested, Hg2+, Zn2+ and Mn2+ strongly inhibited its activity, and Ca2+ stimulated it to some extent.
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