C-type diheme cytochrome, which is part of the SoxAX cytochrome complex involved in sulfur oxidation. The SoxAX complex catalyzes the formation of a heterodisulfide bond between the conserved cysteine residue on a sulfur carrier SoxYZ complex subunit SoxY and thiosulfate or other inorganic sulfur substrates. This leads to the liberation of two electrons, which may be transferred from the SoxAX complex to another cytochrome c that then channels them into the respiratory electron transport chain. Some electrons may be used for reductive CO(2) fixation. 2 Fe(III)-[cytochrome c] + L-cysteinyl-[SoxY protein] + thiosulfate = 2 Fe(II)-[cytochrome c] + 2 H(+) + S-sulfosulfanyl-L-cysteinyl-[SoxY protein] 2 Fe(III)-[cytochrome c] + S-sulfanyl-L-cysteinyl-[SoxY protein] + thiosulfate = 2 Fe(II)-[cytochrome c] + 2 H(+) + S-(2-sulfodisulfanyl)-L-cysteinyl-[SoxY protein] Binds 2 heme c groups covalently per subunit. Heterodimer of SoxA and SoxX. Cysteine persulfide at Cys-220. Belongs to the SoxA family.