Insulin and Glucagon Binding and Degradation by Kidney Cell Membranes*

The binding and degradation of insulin and glucagon to kidney cell membranes was examined. Time- and temperature-dependent specific binding of [125I]iodo-insulin to kidney cell membranes was demonstrated. The membranes also degraded insulin in a time-, temperature-, and protein concentration-dependent manner. The apparent Km of the degradation was 2.7 x 10(-7) M. Glucagon degradation by the kidney membranes was extremely active. Per milligram of protein the kidney membrane was over 20 times as active as the liver membrane. Even at 4 C, significant glucagon degradation occurred. Because of this very active degradation, glucagon binding could not be accurately assessed. The kidney glucagon-degrading activity was inhibited by glutahione and EDTA but unaffected by N-ethylmaleimide, ACTH, or insulin, all potent inhibitors of liver glucagon degradation. The apparent Km for glucagon degradation by the kidney, however, was essentially identical with that for the liver, 2.4 x 10(-6) M.