HUMAN-LIVER ALANINE AMINOPEPTIDASE - A KININ-CONVERTING ENZYME SENSITIVE TO BETA-LACTAM ANTIBIOTICS

Abstract

Human liver alanine aminopeptidase catalyzes the stepwise hydrolysis of methionyl-lysyl-bradykinin to yield methionine, lysine, and the limit nonapeptide, bradykinin, which is resistant to further hydrolytic cleavage by this enzyme. Alanine aminopeptidase also catalyzes the hydrolysis of various neutral amino acid .beta.-naphthylamides. This enzyme cleaves N-terminal arginyl residues unless the adjacent penultimate residue is proline as is the case for bradykinin. The properties are consistent with the requirements of a kinin converting enzyme. Human alanine aminopeptidase activity is reduced by several .beta.-lactam antibiotics, with the cloxacillin, oxacillin, and methicillin Ki values being 0.51, 1.6 and 2.4 mM, respectively. Experiments with radioactively labeled penicillin indicate that 2 mol of antibiotic are bound per mol of enzyme. Neither chromatography of the penicillin-treated enzyme on G-25 Sephadex, treatment of penicillin-G-treated enzyme with penicillinase, nor extensive dilution of cloxacillin-treated enzyme diminished the degree of inactivation produced. Inhibition was obtained with 6-aminopenicillanic acid, which indicated that the pencillin nucleus itself was being bound, but substitutions, as in cloxacillin, could enhance the binding.