Characterization and immunohistologic demonstration of angiotensin-converting enzyme in human renal cell carcinoma

Angiotensin-converting enzyme (ACE, EC 3.4.15.1) was demonstrated in the tissue of human renal cell carcinoma and its cultured cells by immunofluorescence and immunohistochemistry using a specific rabbit antibody to human kidney ACE. The biochemical properties of the partially purified enzyme from the tumor tissue were identical with the pure enzyme from normal kidney with respect to Km, optimal pH, chloride ion activation and heat sensitivity. Catalytic activities of tumor and normal kidney enzymes were similarly inhibited by an ACE inhibitor, captopril, and by the antibody to human kidney ACE. However, double immunodiffusion analysis showed spur-forming immunoprecipitin bands between the tumor and normal kidney enzyme. These data suggest that human renal cell carcinomas have a new isozyme of ACE differing in part immunologically from the enzyme of normal kidney.