Abstract
Angiotensin I-converting enzyme (peptidyl dipeptide hydrolase, EC 3.4.15.1) was solubilized from the membrane fraction of human lung using trypsin treatment and purified using columns of DE 52-cellulose, hydroxyapatite and Sephadex G-200. The purified enzyme was shown to convert angiotensin I to angiotensin II and also to inactivate bradykinin. The specific activity of the enzyme was 9.5 units/mg protein for Hippuryl-His-Leu-OH and 0.665 pmol/min per mg protein for angiotensin I. The enzymic activity obtained after trypsin treatment (1mg/200mg protein) for 2h could be divided into three components:(i) an enzyme of molecular weight 290000 (peak I),(ii) an enzyme of molecular weight 180000 (peak II) and (iii) an enzyme of molecular weight 98000 (peak III), by columns of DE 52-cellulose and Sephadex G-200. Km values of peak I, II and III fraction for Hippuryl-His-Leu-OH were identical at 1.1mM. pH optimum of the enzyme was 8.3 for Hippuryl-His-Leu-OH.
