C-type monoheme 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 and which then 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 1 heme group per subunit. Optimum pH is 6.0-6.5. E(0) is less than -550 mV (at pH 10.0). Optimum temperature is 55-60 degrees Celsius. Heterodimer of SoxA and SoxX. The SoxAX complex interacts with CT1020, SoxAX-binding protein SaxB (SoxK); this interaction seems to be between SoxA and CT1020 and stimulates catalytic activity of the SoxAX complex. Cysteine persulfide at Cys-247. The measured mass is that of mature SoxA with a heme bound and with a cysteine persulfide modification. Belongs to the SoxA family.