Insulin degradation by intact erythrocytes is associated with low-affinity insulin binding sites

The effect of Con A and glucose on insulin binding and receptor-mediated degradation by intact erythrocytes was studied. Con A blocked totally high-affinity insulin binding but did not change low-affinity binding. Glucose at the concentration of 25 mM produced a bidirectional effect; it increased high-affinity insulin binding but decreased low-affinity binding. Con A did not affect receptor-mediated insulin degradation rate. Glucose caused a clear decrement in insulin degradation rate. These results show that insulin degradation by intact erythrocytes is closely associated with the low-affinity insulin receptor. The two-site model for the insulin receptor is favored by the present findings.