A critical appraisal of the effect of oxidized glutathione on hepatic glucose 6-phosphate dehydrogenase activity

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Abstract
Experiments were undertaken to elucidate the mechanism of the reversal of NADPH inhibition of rat liver glucose 6-phosphate dehydrogenase by oxidized glutathione alone and in combination with a putative cofactor described by Eggleston and Krebs (1974). Evidence is presented that this reversal is largely an artifact, caused by the incorrect application of a control assay procedure and a spurious effect of Zn2+ (added in order to inhibit glutathione reductase) in crude enzyme solutions. When the proper assay procedure is used and glutathione reductase is inhibited with low concentrations of Hg2+, glutathione addition has no effect on NADPH inhibition of glucose 6-phosphate dehydrogenase. No evidence was found for the existence of a cofactor that mediates an effect of glutathione on glucose 6-phosphate dehydrogenase.