The effect of sulfhydryl active agents on insulin binding to the erythrocyte insulin receptor

In vitro incubation of human erythrocytes with disulfide reducing agents (dithiothreitol and 2-mercaptoethanol) produces a significant increase in specific binding of 125I insulin to the insulin receptor. Insulin binding is maximal in the presence of 10(-4)M dithiothreitol and declines abruptly at higher concentrations. Preincubation of red cells with these agents and repeated washing prior to inclusion in the receptor assay produced similar effects, but at higher concentrations of reducing agent (10(-2)M dithiothreitol). The increased binding of insulin was consistent with an increase in receptor affinity induced by the reducing agents. Agents which alkylate or oxidise free sulfhydryl groups tended to decrease specific binding of 125I insulin to the receptor. These data suggest that alterations of sulfhydryl groups may be an important mechanism in modulating insulin receptor affinity.