The large-scale isolation of renin-containing granules from rabbit renal cortex by zonal centrifugation

A new method for the isolation of renin-containing granules from rabbit renal cortex by sequential two-dimensional centrifugation is presented. A mitochondrial fraction produced by preparative differential centrifugation was subjected to isopycnic centrifugation on combined discontinuous and linear density gradients in the same SZ-14 reorienting gradient zonal centrifuge rotor. Renin activity, as assayed by radioimmunoassay for angiotensin I, was localized in a region of the density gradient with a corresponding density of 1.196 Gm. per cubic centimeter or 1.53 M sucrose. The renin-containing granules were enriched 5.0-fold over whole homogenate levels, while peroxisomes were enriched 17.4-fold, lysosomes 23.4-fold, and mitochondria 4.3-fold. Electron microscopic examination of the fraction with highest renin activity showed a granular fraction almost free of contamination from other subcellular material. The data supports the view that renin-containing granules are a distinct subcellular particle. This new method for the large-scale isolation of renin-containing granules makes it possible to obtain the quantity of material necessary to study the release renin at the subcellular level and permit the further biochemical purification and characterization of the enzyme.