ISSN:
1573-4919
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
Summary Oxidized glutathione (GSSG) markedly stimulated specific insulin binding, labelled glucose oxidation, and 2-deoxyglucose transport in rat adipocytes in a concentration-dependent manner. Reduced glutathione was inhibitory. Insulin stimulated in the presence of reduced and oxidized glutathione, but the effect was markedly diminished or absent at the highest concentrations of reduced or oxidized tripeptide. Oxidized glutathione did not activate % glycogen synthaseI activity. The stimulation of % glycogen synthaseI activity by insulin was decreased by oxidized glutathione in a concentration-dependent manner. In the presence of glucose, oxidized glutathione minimally activated glycogen synthase, and the stimulation by insulin again was reduced with increased oxidized glutathione concentration. Preincubation of rat adipocytes with N-ethyl-maleimide (NEM) for one minute abolished basal labelled glucose oxidation, basal 2-deoxyglucose transport, and also the insulin-stimulated activities. The concentration of NEM required to inhibit the insulin-stimulated activities (0.2 mM) was considerably lower than that required to inhibit basal activities (0.5 mM and greater), suggesting an involvement of at least two different populations of SH groups. Very short (5 s) preincubation with NEM abolished the stimulation of % glycogen synthaseI observed with insulin. Preincubation of adipocytes with insulin prevented this action of NEM on glycogen synthase indicating a cell membrane site of inhibition by NEM. Increased labelled glucose oxidation and 2-deoxyglycose transport observed with increased oxidized glutathione concentrations, as well as the insulin stimulation, were abolished by preincubation of adipocytes with trypsin or cytochalasin b, suggesting that trypsin-sensitive and cytochalasin B-binding protein(s) presumably in the cell membrane are involved in the activation by oxidized tripeptide. Oxidized glutathione thus acts at the cell membrane as a perturbant to influence cell membrane binding of insulin and hexose transport, but does not act to control intracellular glycogen synthase activation, similarly to the increase in pH, detailed in paper I and distinctly different from trypsin to be discussed in paper III.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02354935
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