Rat renin: purification and characterization.

In order to clarify the molecular basis of the unique features of rat renin (EC 3.4.99.19) and to provide materials and basic information for high blood pressure studies in rats, renin was purified from rat kidney. The final step of purification on CM-cellulose separated renin into three major isoenzyme peaks, R-I, R-II, R-III, and an additional minor peak. These preparations were judged homogeneous by multiple criteria, and the isoenzymes were found to have similar amino acid compositions. The amino acid composition is also closely analogous to hog renin, except that rat renin has a higher cysteine content. In contrast to hog renin, the rat enzymes do not contain amino sugars, yet are apparently glycoproteins as judged by their affinity for concanavalin A. The molecular weights of R-I, R-II, and R-III were estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to be 37 000, 36 000 and 35 000, respectively. The isoelectric points were 5.05, 5.15 and 5.22, respectively. The specific activities of the purified enzymes (determined using rat plasma as substrate) were 615, 626 and 452 Goldblatt units/mg, respectively. Comparison of activities with the hog- and rat-derived substrates indicated a preference for that from the rat. The reaction of the rat enzymes with a synthetic peptide substrate had a similar catalytic rate constant to the hog enzyme, indicating close similarity in the active site region of the two enzymes.