Effect of glutathione on the redox transitions of naphthohydroquinone derivatives formed during DT-diaphorase catalysis.

The oxidation of GSH coupled to the redox transitions of 1,4-naphthoquinone derivatives during DT-diaphorase catalysis was examined. The quinones studied included 1,4-naphthoquinone and its dimethoxy- and hydroxy derivatives and were selected according to their different ability to undergo nucleophilic addition with GSH and the dual effect of superoxide dismutase on hydroquinone autoxidation. GSH was oxidized to GSSG during the redox transitions of the above quinones, regardless of their substitution pattern. This effect was accompanied by an increase of total O2 consumption, indicating the ability of GSH to support quinone redox cycling. The values for the relationship [O2]consumed/[GSSG]formed were, with every quinone examined, above unity, thus pointing to the occurrence of autoxidation reactions other than those involved during GSSG formation. These results are discussed in terms of the functional group chemistry of the quinones and the thermodynamic properties of the reactions involved in the reduction of the semi- to the hydro-quinone by GSH.