Purification and characterization of the neutral endopeptidase from human kidney

The presence of an endopeptidase hydrolyzing succinyl trialanine-p-nitroanilide [Suc(Ala)3-pNA] to Suc(Ala)2 and Ala-pNA in human kidney and its partial characterization have been reported (Ishida et al. (1981) Biochem. Int. 3, 239-246). This neutral metallo-endopeptidase was separated into two fractions (A and B) on Sephacryl S-300 and fraction B was further purified to an electrophoretically pure state. The fraction B enzyme had a molecular weight of 100,000 and was inhibited by metal chelators such as EDTA, o-phenanthroline and phosphoramidon, but not by serine protease inhibitors. The enzyme was found to hydrolyze peptide bonds preferentially at the amino sides of hydrophobic amino acids such as Leu and Phe, when its specificity was studied using insulin B chain and angiotensin I. Fraction A seems to be a tetramer of fraction B, judging from its molecular weight, pI, substrate specificity and immunological properties.