The function and the structural features of Chromatium vinosum cytochrome c-552 have been investigated. Cytochrome c-552 has a sulfide-cytochrome c reductase activity and also catalyzes the reduction of elementary sulfur to sulfide with reduced benzylviologen as the electron donor. In the sulfide-cytochrome reduction, horse and yeast cytochromes c act as good electron acceptors, but cytochrome c' or cytochrome c-553(550) purified from the organism does not.
The subunit structure of cytochrome c-552 has been studied. The cytochrome is split by 6M urea into cytochrome and fiavoprotein moieties with molecular weights of 21, 000 and 46, 000, respectively. The fiavoprotein moiety is obtained by isoelectric focusing in the presence of 6M urea and 0.1% β-mercaptoethanol, while the hemoprotein moiety is obtained by gel filtration with Sephacryl S-200 in the presence of 6 M urea and 0.1M KCl. Neither subunit has sulfide-cytochrome c reductase activity. Attempts to reconstitute the original fiavocytochrome c from the subunits have been unsuccessful.