| Abstract: | Crude renin granule preparations isolated from the rat renal cortex were further purified in isotonic conditions (300 mOsm/kg) using various density gradient materials. It was not possible to separate renin granules from other subcellular organelles using dextran, 40,000-sucrose or metrizamide-sucrose gradients at about 300 mOsm/kg. When osmolality of dextran-sucrose gradients was increased, some separation was found but both renin granules and mitochondria gained density. During a short centrifugation (4640 X g, 30 min) renin granules remained intact and appeared in two populations in Percoll-sucrose gradients. The apparently heavier (larger) particles (at 1.12-1.13 kg/l) were greatly purified from mitochondria (80 X purification vs. the whole homogenate), protein (120 X) and lysosomes (24 X). Electron micrographs demonstrated many dense core granules. The fraction containing apparently lighter (small) granules (at 1.08-1.09 kg/l) was heavily contaminated with mitochondria and lysosomes. During longer centrifugation (4640 X g, 60 min), only one major peak showing renin activity was observed at 1.12-1.13 kg/l, and other cell organelles were lighter. Hence the two renin populations evidently do not differ in density but rather in size. In the animals kept on a low-sodium diet, both types of renin granules were increased. |
