Characteristics of human erythrocyte insulin-like growth factor I receptors.

The scarcity of purified materials has prevented studies of the mechanism of insulin-like growth factor I (IGF-I) action. Recently, an IGF-I analog, Thr59-IGF-I, was synthesized by recombinant DNA technology. We found that this analog had binding characteristics similar to those of natural IGF-I in the radioreceptor assay system. We used this analog to characterize human erythrocyte IGF-I receptors as follows. Erythrocytes from 33 normal subjects specifically bound 6.9 +/- 0.7% (mean +/- SD)/2.8 X 10(9) cells/ml. Scatchard analysis of the binding data showed that the total number of receptors per erythrocyte was 13, and the affinity constant was 1.26 X 10(9) M-1, similar to that of other human IGF-I receptors previously reported. We also examined IGF-I receptors in patients with insulin receptor abnormalities. Although the specific values of IGF-I binding to erythrocytes were decreased or increased in parallel with those of insulin, the degrees of decrease or increase were much smaller. This suggests that the expression of insulin receptors and that of IGF-I receptors are discordant.