Abstract
The substrate specificity of a purified kidney neutral endopeptidase was studied. The endopeptidase hydrolyzed a variety of biologically active peptides, such as angiotensins (angiotensins I, II and III), bradykinins (bradykinin, Lys-bradykinin, Met-Lys-bradykinin and des-9Arg-bradykinin), enkephalins (Leu-enkephalin and Met-enkephalin), neurotensin and substance P, and was found to cleave only the bonds at the amino side of hydrophobic amino acids in the peptides. However, when a hydrophobic amino acid was present at the C-terminus or at the position adjacent to the N-terminus, the bond of the hydrophobic residue was not cleaved. In further studies on the degradation of a series of homo-oligopeptides, the enzyme appeared to hydrolyze those consisting of at least a tetrapeptide unit of hydrophobic amino acids such as Ala and Phe. The specificity of the membrane-bound neutral endopeptidase from rat kidney indicated by these results can be summarized as follows : the enzyme requires at least a tetrapeptide unit for hydrolysis, and cleavage occurs only at the amino side of a hydrophobic amino acid, when one is present at the third position of the tetrapeptide unit.
