Isolation of Renin Granules from Rat Kidney Cortex and Evidence for an Inactive Form of Renin (Prorenin) in Granules and Plasma

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Abstract
Renin was demonstrated in particles having a sedimentation velocity similar to that of mitochondria during differential centrifugation. Further purification by isopycnic gradient centrifugation separated renin granules from the bulk of mitochondria and lysosomes, and from microsomes and cytoplasm. The density of renin granules was 1.202, which differed from the mean equilibrium densities of mitochondria (1.175) and lysosomes (1.170 and 1.230) in the heavy granule fraction. In studies involving gel filtration and polyacrylamide gel electrophoresis, renin granules appeared to contain an inactive form of renin that could be activated by acid treatment, had a higher apparent MW than renin, and may be a more basic molecule. Inactive renin was also studied in plasma by electrophoresis and may originate from renin granules after exocytosis by the juxtaglomerular cells. Inactive renin may be a biosynthetic precursor (prorenin) and may be activated within the cell by a specific protease consequent upon the fusion of renin granules with lysosomes, providing a mechanism for the rapid regulation of renin activity prior to secretion.

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