Diheme cytochrome c which may be involved in sulfate reduction. Binds 2 heme c groups per subunit. Each heme is also bound by the other subunit. Binds 1 iron-sulfur cluster per subunit, probably [2Fe-2S] cluster. E(0) are -168 mV and -330 mV. Homodimer; linked through the 4 hemes that are shared between the subunits. The N-terminal Gly is blocked by a labile group with a mass of 85 Da. Predicted to be exported by the Tat system.