The storage form of renin in renin granules from rat kidney cortex

Renin granules were partially purified from rat kidney cortex, and a storage form of renin in the granules was examined. Renin granules were isolated by discontinuous Percoll density gradient centrifugation followed by continuous Percoll density gradient centrifugation. The partially purified fraction was free from mitochondria and microsomes, as judged by the absence of marker enzymes of these organelles, but contained some lysosomal enzyme activities. The specific renin activity was 0.58 mg angiotensin I/hr/mg protein, 500 times as active as the original homogenate. Immunochemical staining with specific antisera against rat kidney renin revealed that about 10% of the granules recovered in the partially purified fractions were stained strongly. The stored renin was not activated either by acidification or by trypsin treatment, indicating that stored renin was in the fully active form. By sodium dodecyl sulfate gel electrophoresis, the stored renin had two different molecular weights, 38,000 and 36,000, and these molecular weights were not reduced by dithiothreitol or 2-mercaptoethanol, suggesting that these renins are single-chain types as opposed to the two-chain type found in male mouse submaxillary gland. These results suggest that active renins with two different molecular weights may be released from renin granules of juxtaglomerular cells.