Interconversion between [2Fe-2S] and [4Fe-4S] cluster glutathione complexes.

We present here how different iron-sulfide-glutathione ratios, applied in conditions comparable to those present in the mitochondrial matrix, affect the speciation of iron-sulfur cluster glutathione complexes. An excess of sulfide with respect to iron ions promotes the formation of a tetranuclear [FeFeS(GS)] complex, while an excess of iron ions favors the formation of a dinuclear [FeFeS(GS)] complex. These two complexes establish an interconversion equilibrium. The latter might play a role in the composition of the mitochondrial labile iron pool potentially contributing to the regulation of cellular iron homeostasis.