Purification and properties of aminopeptidase and arylamidase from human liver

Aminopeptidase and arylamidase from human liver were purified 1,580- and 1,130-fold, respectively, by ammonium sulfate fractionation, TEAE-cellulose and hydroxylapatite column chromatographies, and Sephadex G-200 gel filtration. The purified preparations appeared to be homogeneous on polyacrylamide gel electrophoresis. The molecular weights of aminopeptidase and arylamidase were determined to be 280,000 and 170,000, respectively, by gel filtration on Sephadex G-200. Aminopeptidase showed marked specificities for amino acid amides, such as L-leucineamide, L-phenylalanineamide, and L-methionineamide. On the other hand, arylamidase showed specificities for amino acid beta-naphylamides, such as L-alanyl-beta-naphthylamide and L-leucyl-beta-naphthylamide, but it also hydrolyzed amino acid amides to a considerable extent. Immunological studies using antibodies to purified aminopeptidase and arylamidase showed that the antigenicities of these two enzymes were different. Neuraminidase treatment of the purified arylamidase changed its isoelectric point from 3.25 to 4.95. Various properties (Km values, optimum pH, substrate specificities, and antigenicity) of the arylamidase were not changed by neuraminidase treatment, but the enzyme became thermo-labile.