Sulfane-activated reduction of cytochrome c by glutathione.

The inorganic sulfane tetrathionate (-O3SSSSO3-) resembles glutathione trisulfide (GSSSG) in that it remarkably activates the reduction of cytochrome c by GSH, both under aerobic and anaerobic conditions. These observations can be explained by the formation of the persulfide GSS-, due to nucleophilic displacements of sulfane sulfur. The GSS- species has previously been proposed to act as a chain carrier in the catalytic reduction of cytochrome c, and perthiyl radicals GSS., formed in the reduction step, were thought to recycle to sulfane via dimerization to GSSSSG.2 The present study provides some arguments in favour of a chain mechanism involving the GSS. + GS-<-->(GSSSG).- equilibrium and sulfane regeneration by a second electron transfer from (GSSSG).- to cytochrome c. Thiosulfate sulfurtransferase (rhodanese) is shown to act as a cytochrome c reductase in the presence of thiosulfate and GSH, and again the generation of GSS- can be envisaged to explain this result.