Structure of the Human Erythrocyte Insulin Receptor

The structure of the insulin receptor in intact human erythrocytes was defined using the techniques of disuccinimidyl suberate (DSS) cross-linking of ¹²⁵I-insulin and surface [125I]iodination followed by receptor immunoprecipitation. In contrast to a recent report, we found the erythrocyte insulin receptor to be similar in structure to that in classic target tissues for insulin, consisting of at least three species of molecular weight approximately 295,000, 265,000, and 245,000, containing disulfide-linked subunits of molecular weight approximately 130,000 and 95,000. The interconversion of the three oligomeric forms could mediate changes in receptor affinity as postulated in other tissues. The 95,000 subunit was detected by immunoprecipitation only if surface iodination was performed in a Tris/Hepes buffer using lodogen and not if phosphate-buffered saline or lactoperoxidase iodination was used. These findings indicate that the lack of a bioeffect of insulin in erythrocytes is not explained by a gross defect in the structure of their insulin receptors. The apparent identity of the insulin receptor structure in erythrocytes and insulin target tissues provides a firmer basis for the use of erythrocytes in some circumstances to reflect insulin receptor status.