 pcrC is a believed to be a c-type cytochrome that connects the AB complex to the membrane and allows for electron shuttling.The function of pcrD is uncertain, but may encode a molybdenum-containing chaperone protein specific to assembling the pcrABC system.All known functional perchlorate reductase enzymes include genetically similar versions of pcrABCD except for the epsilonproteobacteria "Arcobacter" strain CAB, which lacks a traditional pcrC and appears to have replaced it with an unrelated epsilonproteobacteria cytochrome.