Abstract

A dipeptide hydrolase was purified 200-fold from hog plasma and concentrated from homogenates of lung and kidney. Guinea-pig plasma is a very rich native source of the enzyme, but the highest specific activity was found in a particulate fraction of the kidney. The enzyme has a dual function: it converts angiotensin I into angiotensin II, and it inactivates bradykinin by cleaving off the C-terminal dipeptides His-Leu or Phe-Arg, respectively. Thus, kininase II is also an angiotensin I converting enzyme. In addition, this enzyme released C-terminal dipeptides from five other shorter peptide substrates. Three of them were used as substrates in ultraviolet spectrophotometric experiments. The activity of dipeptide hydrolase was inhibited by ethylenediamine tetraacetic acid, and several divalent metal ions restored its activity. It was also inhibited by the dipeptide split products of the reactions, by a pentapeptide, by insulin and by the B chain of insulin.