Stabilization of insulin receptor subunit structure by glutathione-insulin transhydrogenase

Abstract A partially purified insulin receptor preparation from rat liver was incubated at 37°C with and without the protein-disulfide interchange enzyme, glutathione-insulin transhydrogenase (thiol: protein-disulfide oxidoreductase/isomerase, EC 1.8.4.2/5.3.4.1). Insulin-binding activity was then assessed by crosslinking receptor- 125 I-insulin complexes and subjecting them to electrophoresis on SDS-polyacrylamide gels in the absence and presence of reductant followed by autoradiography. Prior incubation of the receptor at 37°C in the absence of the enzyme markedly decreased the subsequent binding of 125 I-insulin to the holoreceptor ( M r 350 000) and to its subunits ( M r 180 000 and 130 000), while addition of the enzyme to the preincubation medium served to substantially prevent this decrease. The loss in binding at 37°C was not restored by subsequent addition of the enzyme, nor was the loss prevented by any of the several known inhibitors of proteolysis. The apparent stabilization of receptor by transhydrogenase, as evidenced by the increase in binding above control levels, was proportional to both the enzyme concentration and the duration of incubation. These effects seem to be specific for transhydrogenase, since several other disulfide-containing proteins were found to be ineffective. These data suggest that the stabilization of the subunit structure of the insulin receptor at physiological temperatures may take place via a disulfide interchange reaction catalyzed by glutathione-insulin transhydrogenase.