Enrichment and Functional Reconstitution of Glutathione Transport Activity from Rabbit Kidney Mitochondria: Further Evidence for the Role of the Dicarboxylate and 2-Oxoglutarate Carriers in Mitochondrial Glutathione Transport

Abstract

In previous studies, we provided evidence for uptake of glutathione (GSH) by the dicarboxylate and the 2-oxoglutarate carriers in rat kidney mitochondria. To investigate further the role of these two carriers, GSH transport activity was enriched from rabbit kidney mitochondria and functionally reconstituted into phospholipid vesicles. Starting with 200 mg of mitoplast protein, 2 mg of partially enriched proteins were obtained after Triton X-114 solubilization and hydroxyapatite chromatography. The reconstituted proteoliposomes catalyzed butylmalonate-sensitive uptake of [14C]malonate, phenylsuccinate-sensitive uptake of [14C]2-oxoglutarate, and transport activity with [3H]GSH. The initial rate of uptake of 5 mM GSH was approximately 170 nmol/min per mg protein, with a first-order rate constant of 0.3 min−1, which is very close to that previously determined in freshly isolated rat kidney mitochondria. The enrichment procedure resulted in an approximately 60-fold increase in the specific activity of GSH transport. Substrates and inhibitors for the dicarboxylate and the 2-oxoglutarate carriers (i.e., malate, malonate, 2-oxoglutarate, butylmalonate, phenylsuccinate) significantly inhibited the uptake of [3H]GSH, whereas most substrates for the tricarboxylate and monocarboxylate carriers had no effect. GSH uptake exhibited an apparent Km of 2.8 mM and a Vmax of 260 nmol/min per mg protein. Analysis of mutual inhibition between GSH and the dicarboxylates suggested that the dicarboxylate carrier contributes a somewhat higher proportion to overall GSH uptake and that both carriers account for 70 to 80% of total GSH uptake. These results provide further evidence for the function of the dicarboxylate and 2-oxoglutarate carriers in the mitochondrial transport of GSH.