Acid angiotensinase as a lysosomal enzyme.

Abstract

1. Both acid angiotensinase and calcium-dependent neutral angiotensinase are widely distributed among various tissues of the rat. High activity of acid angiotensinase in such lysosome-rich tissues as kidney, spleen and liver suggests localization of this enzyme in lysosomes. 2. Main angiotensinases in rat liver are concentrated in lysosomal and soluble fractions. The lysosomal enzyme which is inhibited by DFP is acid angiotensinase, while the other is calcium-dependent neutral angiotensinase. 3. The pH optimum of lysosomal angiotensinase of the kidney is 5.6-5.7. Properties of acid angiotensinase indicate that a carboxypeptidase, so-called angiotensinase C, is a lysosomal eazyme and plays a main role in lysosomal angiotensinase activity. On the other hand, partial inhibition and activation by p-chloromercuribenzoate and dithiothreitol imply that some other enzyme(s) may take part in this activity. 4. Acid angiotensinase of kidney lysosomes was separated from arylamidase and hemoglobin-splitting cathepsin by Sephadex gel-filtration. Cathepsin A activity, however. Could not be eliminated from the acid angiotensinase by either Sephadex gel-filtration or DEAE-cellulose Column chromatography. DFP showed an inhibitory effect on cathepsin A activity of kidney lysosomes. 5. Molecular weight of lysosomal acid angiotensinase of rat kidney is between 70, 000 and 90.000, calculated by Sephadex gel-filtration. 6. Possible role of the lysosomal enzyme in angiotensin metabolism in vivo is discussed.