Insulin binding and degradation by kidney cell membranes of streptozotocin-diabetic rats.

The interaction of insulin with purified rat kidney cell membranes was studied with the use of 125I-insulin. The membranes showed high insulin-degrading activity which was dependent on temperature, time and membrane concentration. Specific binding of insulin was demonstrated in the presence of 0.3 mM bacitracin and was time- and temperature-dependent. 125I-insulin was displaced by native insulin, AI-B29 dodecoyl insulin and proinsulin in proportion to their relative bioactivity. Kidney membranes isolated from streptozotocin-diabetic rats bound more insulin per mg of membrane protein (approx. 65%) than did membranes of control animals. Scatchard analysis indicated that this increase in binding was due to an increased binding capacity rather than an increased affinity for insulin. Injection of diabetic rats with insulin resulted in a decrease of insulin binding when compared with the untreated diabetic animals. Diabetes also resulted in altered kinetics of insulin degradation.