Purification and Some Properties of Two Aminopeptidases from Sardines

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Two fish aminopeptidases designated as aminopeptidases I and II were purified by DEAE-cellulose chromatography, gel filtration on Sephadex G-200, and isoelectric focusing. The final preparations of enzymes I and II were judged nearly homogenous by polyacrylamide gel electrophoresis. The molecular weights of enzymes I and II were determined by gel filtration to be 370, 000 and 320, 000, respectively. The isoelectric points were 4. 1 (I) and 4.8 (II). Both enzymes were inhibited by EDTA and activated by Co++. Bestatin could inhibit enzyme I but not enzyme II. Enzymes I and II rapidly hydrolyzed not only synthetic substrates containing alanine or leucine but also di-, tri-, and tetra-alanine. Judged from all of these properties, sardine aminopeptidases resemble human alanine aminopeptidase. Enzyme I retained more than 70% of its original activity in 15% NaCl, suggesting the enzyme participates in hydrolyzing fish proteins and peptides during fish sauce production.
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