A novel diisopropylphosphofluoridate-sensitive phenylalanine arylamidase in human liver

A diisopropylphosphofluoridate-sensitive (DFP-sensitive) arylamidase, which preferentially hydrolyzed Phe-p-nitroanilide (Phe-pNA), was purified from a crude extract of human liver by conventional chromatographic techniques. The purified enzyme gave a single band on SDS-polyacrylamide gel electrophoresis. The molecular weight of the enzyme was estimated to be 58,000 by SDS-polyacrylamide gel electrophoresis and 200,000 by chromatography on a column of Sephacryl S-300, suggesting that the enzyme is a trimer or a tetramer. The enzyme was inactivated in proportion to the amount of [3H]DFP incorporated with a [3H]DFP/subunit (58,000) molar ratio of 1.04. The data indicate that the enzyme belongs to the serine protease family.