Angiotensinase with a high degree of specificity in plasma and red cells.

A peptidase with a high degree of specificity for angiotensin II occurs in normal human plasma and red cells. Preparations from both sources have the same pH optimum, require calcium ions, and hydrolyze valyl(5)- or isoleucyl(5)-angiotensin II, but do not hydrolyze beta-aspartyl(1)-angiotensin II, arginyl(1)-angiotensin II or deaminoangiotensin II. This enzyme, given the name angiotensinase A, requires alpha-L-aspartic acid or alpha-L-asparagine as the N-terminal amino acid in its angiotensin substrate, and thus differs from kidney leucine aminopeptidase. Other peptidases known to hydrolyze angiotensin also hydrolyze at least one of the other angiotensin analogs with substitution in the one position.