Rat liver microsomal glucose-6-P translocase. Effect of physiological status on inhibition and labeling by stilbene disulfonic acid derivatives.

Intact microsomes from groups of fed, fasted, glucocorticoid-treated (triamcinolone) and diabetic (alloxan) rats were reacted with 4,4'-diisothiocyanostilbene-2,2'-disulfonic (DIDS), a specific inhibitor of microsomal glucose-6-P translocase. The concentrations that inhibit by 50% were 41 +/- 2, 31 +/- 1, 39 +/- 4, and 18 +/- 1 microM (mean +/- S.E.; n = 3); (order as above). The maximal levels of inhibition of the translocase by DIDS were 66 +/- 2, 79 +/- 2, 63 +/- 1, and 88 +/- 1%, respectively. The differences in the values for the different groups of animals are statistically significant, except for comparisons between fed and triamcinolone-treated animals. Microsomes from the same groups of animals were treated with the tritiated reduced derivative of DIDS, [3H]H2DIDS, which labels a 54,000-dalton polypeptide, previously implicated as a component of the glucose-6-P translocase. The mean values (+/- S.E.) of [3H]H2DIDS bound to the polypeptide under saturating conditions were 100 +/- 6, 120 +/- 9, 62 +/- 7, and 101 +/- 15 pmol/mg of microsomal protein, respectively. The amount bound in microsomes from triamcinolone-treated rats is significantly lower from the values for the other three physiological states, which do not differ significantly from each other. The presence of glucose-6-P, but not mannose-6-P, during the [3H]H2DIDS reaction significantly stimulates the labeling of the 54,000-dalton polypeptide in microsomes from all the classes of animals above, except the diabetic animals. These results indicate that DIDS and [3H]H2DIDS are probes sensitive enough to discern differences in the translocase due to physiological regulation. On the basis of the labeling studies with [3H]H2DIDS, the increase in translocase activity observed in microsomes from fasted, triamcinolone-treated, and diabetic rats cannot be ascribed to increased numbers of translocase molecules, but rather to increased functional activity of the translocase protein.