Purification and properties of an aminopeptidase from mullet, Mugil cephalus, Roe.

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Abstract
An aminopeptidase was purified from an aqueous extract of mullet roe in the presence of 2-mercaptoethanol by fractionation with ammonium sulfate and column chromatography on DEAE-cellulose and Sephadex G-200. The molecular weight of the enzyme was 184, 000 by gel filtration, and the enzyme appeared to consist of two homogenous subunits. The optimal pH and optimal temperature for activity were 7.4 and 45°C, respectively. Puromycin, p-chloromercuribenzoic acid, and o-phenanthroline inhibited the enzyme n on-competitively (their Ki=1.34μM, 0.113mM and 0.145mM, respectively), while 2-mercaptoethylamine was competitive (Ki = 0.056 mM). The enzyme was also inhibited by L-amino acids, in particular glutamic acid. The enzyme could hydrolyze a variety of α-aminoacyl β-naphthylamides and was most active on L-alanyl-β-naphthylamide. Judging from these properties, the mullet roe aminopeptidase resembles soluble alanyl aminopeptidase [EC 3.4.11.14].

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