A tetraheme cytochrome c 3 was purified from extracts of Desulfobulbus elongatus. Redox potentiometry studies indicated that one of the four hemes has a uniquely high E m value (−30 mV), whereas the other three have a lower redox potential with E m values of −165 mV. In the presence of a membrane preparation from Db. elongatus the cytochrome c 3 is partially reduced (23% at pH 7.6) by succinate. The physiological significance of the high redox potential of this cytochrome c 3 is discussed as a function of the propionate metabolism of Desulfobulbus which is known to proceed via the succinate pathway.
