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 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 1 heme c group covalently per subunit. Contains a mononuclear Cu(II) center. Activated by free Cu(II) ions and pH values above 8. kcat is 8.72 sec(-1) and 5.7 sec(-1) for glutathione at pH 6.0 and pH 7.0, respectively. E(0) is -479 mV for heme at pH 8.0 (PubMed:21592966). E(0) is -430 mV for heme at pH 6 with copper-loaded SoxAX, -455 mV for heme at pH 7 with copper-loaded SoxAX, -486 mV for heme at pH 8 with copper-loaded SoxAX, -424 mV for heme at pH 6 with copper-free SoxAX, -479 mV for heme at pH 7 with copper-free SoxAX, -507 mV for heme at pH 8 with copper-free SoxAX (PubMed:18552405). E(0) is -196 mV for copper center. The Fe (III/II) potentials are +133 mV at pH 6.0, +104 mV at pH 7.0, +49 at pH 7.9 and +10 mV at pH 8.7. Heterodimer of SoxA and SoxX. Cysteine persulfide at Cys-236. The measured mass is that of mature SoxA with a heme bound and without a cysteine persulfide modification. The measured mass is that of mature SoxA with a heme bound and with a cysteine persulfide modification. Belongs to the SoxA family. Extended N-terminus.