Purification and some properties of two aminopeptidases from sardines.

Two fish aminopeptidases designated as aminopeptidases I and II were purified by DEAEcellulose chromatography, gel filtration on Sephadex G-200, and isoelectric focusing.The final preparations of enzymes I and II were judged nearly homogenousby 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 EDTAand 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 humanalanine aminopeptidase.EnzymeI retained morethan 70%of its original activity in 15% NaCl, suggesting the enzyme participates in hydrolyzing fish proteins and peptides during fish sauce production.