Relation Between the Activities Reducing Disulfides and the Protection Against Membrane Permeability Transition in Rat Liver Mitochondria

The oxidation of some mitochondrial sulfhydryl groups acts as an inducer of the mitochondrial membrane permeability transition. This membrane damage can be reversed by regeneration of the sulfhydryl groups. Hence the mitochondrial activities reducing disulfides are especially important for the defense against oxidative injury. The ability of isolated rat liver mitochondria to reduce disulfides was examined by the reduction of 5,5'-dithiobis-(2 nitro-benzoic acid) (DTNB), the reaction catalyzed by thioredoxin reductase and glutathione reductase. The incubation of mitochondria with DTNB induced their swelling which was prevented by EGTA, cyclosporin A, Mg2+, and pyrophosphate. The rate of DTNB reduction by mitochondria was compared with the changes in their volume and in the total content of their sulfhydryl groups. The reduction of DTNB was stimulated by cation chelators, both unphysiological and physiological, and was suppressed by up to 65% during mitochondrial swelling. In mitochondria treated with tert-butylhydroperoxide the total content of mitochondrial sulfhydryl groups decreased in the correlation with the suppression of DTNB reduction and with mitochondrial swelling. The content of nonprotein sulfhydryl groups was significantly lowered under all conditions applied. However, the protein sulfhydryl groups were preserved in the presence of EGTA or Mg2+ when the rate of DTNB reduction was relatively high and this was associated with the strong inhibition of mitochondrial swelling. It is suggested that during oxidative stress mitochondrial activities reducing disulfides are involved in the maintenance of sulfhydryl groups in mitochondria thus protecting their membranes against permeabilization.