Isolation of protein bodies on sucrose gradients.

Storage protein bodies from sunflower cotyledons during early stages of seed germination were isolated on sucrose density gradients by isopycnic centrifugation. The density of this organelle on the gradients ranged between 1.26 and 1.36 g cm(-3). A proteinase with a pH optimum of 5.2 was associated with this organelle, and is probably responsible for degradation of storage protein. A NADH-dependent cytochrome-c reductase, a membrane marker enzyme with a pH optimum of 8.4, was also present in this organelle fraction.