Dependence of insulin degradation by intact erythrocytes on receptor binding in diabetic patients.

Degradation of insulin during incubation of erythrocytes at 37 degrees C was studied in relation to insulin binding to membrane receptors. A method was developed for measuring separately the degradation caused by insulinase released from leaky cells into the incubation medium, and the degradation generated by intact cells. In the 23 samples studied, intact erythrocytes generated 16-41%, and cell-free insulinase the rest, 59-84%, of the amount of insulin degradation products formed during 40 min of incubation. The number and affinities of insulin receptors, and the degradation of insulin by intact erythrocytes, were measured in samples from 23 patients with glucose intolerance. Degradation rate correlated well with the receptor number and to a lesser degree with the affinities. The results suggest that insulin binding is a regulatory step for the formation of insulin degradation products.