Formation of Bradykinin from Kallidin-10 by Aminopeptidase B

Abstract

AMINOPEPTIDASE B is a mammalian enzyme selective for the N-terminal arginine and lysine residues of peptides. This enzyme has been described, purified and characterized^1–3. It occurs in many of the organs of the rat and other species and, like cathepsin C, is known to be activated markedly by chloride ions. Aminopeptidase B is almost inactive in the complete absence of these ions and shows maximal activity at physiological concentrations of chloride. The physiological role of the enzyme was unknown, and an effort was made to determine whether some naturally occurring N-terminal arginine and lysine peptides could be split by the enzyme. A peptide of this type, kallidin-10, is liberated from the serum α₂-globulin fraction by proteolytic enzymes such as trypsin and kallikrein. Bradykinin is formed when the N-terminal lysine of kallidin-10 is released. Bradykinin has an N-terminal arginine adjacent to proline. Our results show that kallidin-10 is transformed to bradykinin by aminopeptidase B without further degradation (liberation of arginine) of the nonapeptide.