Degradation of Insulin and Glucagon in Homogenates and Subcellular Fractions of Isolated Pancreatic Islets

Summary

¹²⁵l-labelled insulin was degraded by islet homogenates in the presence of GSH by an initial reductive cleavage of its disulfide bonds and, subsequently, by proteolytic degradation of the single chains. The proteolytic degradation of insulin was measured directly using the sensitive fluram method. The proteolysis of both insulin and glucagon occurs mainly in the cytosol and to a lesser extent in the fraction of nuclei and cell debris. Evidence is given for the presence of lysosornes in pancreatic islets.

Studies on insulin secretion by RENOLD (1) have shown that intracellular insulin catabolism seems to play an important part in regulating the hormone content of pancreatic islets. In several tissues insulin is catabolized by a reductive cleavage of its disulfide bounds and, subsequently, by a proteolytic degradation (2,3). We investigated the insulin and glucagon degradation in pancreatic islets in vitro.