QUANTITATION OF THE CLASS-I DISULFIDES OF THE INSULIN-RECEPTOR

The disulfide structure of the insulin receptor was probed using dithiothreitol and [3H]-N-ethylmaleimide to reduce purified human placental receptor and label the cysteine residues. After protein quantitation, the amount of radioactivity in both the α and β subunits was counted for each of the three species generated: native dimer, reduced receptor which remained covalently dimeric, and reduced monomer. It was found that the native receptor contained only one sulfhydryl group, on the β subunit; the reduced dimer contained one new sulfhydryl on each α subunit, and the α subunit of the monomer contained two sulfhydryls. This suggests a simple model for the receptor class I disulfides. © 1991.