CcmB is the product of one of a cluster of Ccm genes that are necessary for cytochrome c biosynthesis in eubacteria. Expression of these proteins is induced when the organisms are grown under anaerobic conditions with nitrate or nitrite as the final electron acceptor. CcmB is required for the export of haem to the periplasm.

1: Escherichia coli genes required for cytochrome c maturation. Thony-Meyer L, Fischer F, Kunzler P, Ritz D, Hennecke H; J Bacteriol 1995;177:4321-4326. PMID:7635817