Tetrahaem cytochrome domain <p>Flavocytochrome C3 (Fcc3) enzymes from a number of Shewanella species, including <taxon tax_id="318167">Shewanella frigidimarina</taxon> (strain NCIMB 400), have respiratory fumarate reductase activity, which enables the bacteria to respire anaerobically with fumarate as a terminal electron acceptor. Flavocytochrome C3 in S. frigidimarina is a soluble, single chain tetrahaem enzyme found in the periplasm, making it distinct from other bacterial fumarate reductases (<db_xref db="INTERPRO" dbkey="IPR010960"/>), which are membrane-bound, multi-subunit enzymes, even though their function is analogous. Shewanella Fcc3 is composed of three domains: an N-terminal tetrahaem cytochrome domain, a flavin domain and a clamp domain. The cytochrome domain can also occur on its own in some tetrahaem cytochromes implicated in iron oxidation. This entry represents the cytochrome domain, which has a different arrangement of the polypeptide chain in comparison to classical tetra-haem cytochrome C3 [<cite idref="PUB00016225"/>, <cite idref="PUB00016226"/>].</p>