Probably transfers electrons from a membrane-associated electron donor (e.g. the membrane quinone pool) to the [4Fe-4S] cluster of the Cgr2 reductase via its covalently bound heme groups. May form a membrane-associated complex with Cgr2. Is highly up-regulated by digoxin and other cardiac glycosides containing unsaturated butyrolactone rings, such as digitoxin, digoxigenin, and, to a lesser extent, ouabain. Is repressed by arginine but not by ornithine. Part of an operon that consists of cgr1 and cgr2. Binds 5 heme groups per subunit. Belongs to the multiheme cytochrome c family.