Cytochrome c4 can be involved in the photosynthetic electron transfer system in the purple bacterium Rubrivivax gelatinosus.

Three periplasmic electron carriers, HiPIP and two cytochromes c8 with low- and high-midpoint potentials, are present in the purple photosynthetic bacterium Rubrivivax gelatinosus. Comparison of the growth rates of mutants lacking one, two, or all three electron carrier proteins showed that HiPIP is the main electron donor to the photochemical reaction center and that high-potential cytochrome c8 plays a subsidiary role in the electron donation in photosynthetically growing cells. However, the triple deletion mutant was still capable of photosynthetic growth, indicating that another electron donor could be present.