Low molecular weight alanine aminopeptidase of human serum: separation and some characteristics

An alanine aminopeptidase, which has characteristics different from those of known alanine cleaving aminopeptidases, was partially purified from human serum by Sephadex G-200 gel chromatography and DEAE Sepharose column chromatography. The enzyme exhibited a molecular weight of 58,000 by gel chromatography. The pI of the enzyme was 5.0, and it was inactivated at 60 degrees C in 20 min. The enzyme readily hydrolyzed L-alanine beta-naphthylamide, but hardly hydrolyzed the other tested beta-naphthylamides. The Km value for L-alanine beta-naphthylamide was 0.29 mM, the pH optimum 7.5. The activity of the enzyme was enhanced by chloride ions and by sulfhydryl ethylenediaminetetraacetic compounds, and was inhibited by sulfhydryl blocking ethylenediaminetetraacetic agents, and bestatin. Furthermore, 1.10 phenanthroline and ethylenediaminetetraacetic acid were inhibitory, and the activity was restored by CoCl2 and ZnCl2. The enzyme is a chloride-enhanced thiol dependent metalloaminopeptidase.