Sulfane-Activated Reduction of Cytochrome c by Glutathione

Abstract

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.

Key Words:

• Cytochrome c reduction
• glutathione free radicals
• perthiyl radicals
• rhodanese
• tetrathionate
• thiosulfate sulfurtransferase