Disulfide exchange between insulin and its receptor. A possible post-binding step in insulin action

A fraction of the insulin specifically bound to adipocytes undergoes a disulfide interchange with its receptor (Clark, S., and Harrison, L. C. (1982) J. Biol. Chem. 257, 12239-12244). In order to test the hypothesis that this covalent modification is a relevant step in insulin action, we have examined the relationship between disulfide binding of insulin and several insulin bioeffects, using sulfhydryl group blocking reagents as probes. The half-time of disappearance of disulfide linked insulin-receptor complexes (I-(S-S)-R) was rapid (4.5 min), consistent with their hypothesized role. A cell-impermeable reagent 5,5'-dithiobis(nitrobenzoic acid) (DTNB) had no effect on specific insulin binding but caused a dose-dependent decrease in both I-(S-S)-R and insulin-stimulated glucose transport. DTNB also inhibited the effect of insulin to stimulate glucose oxidation and to inhibit epinephrine-stimulated cyclic AMP production. In cultured IM-9 lymphocytes, insulin-induced down regulation of its receptor was decreased by 75% in the presence of 1 mM DTNB. Receptor antibodies stimulated adipocyte glucose transport maximally but their effect, unlike that of insulin, was not inhibited by DTNB. These findings suggest that receptor sulfhydryl groups are required for insulin action and support the notion that their interchange with insulin is a necessary step in activation of postreceptor pathways.