Type c Cytochrome, Rhodospirillum, Bacterium Chlorobium,Nonsulphur Bacterium Rhodospirillum Rubrum,Green Sulphur Bacterium Chlorobium

Type c Cytochrome

	Type c Cytochrome - A number of different c type cytochromes have been found in the electron transport system of photosynthetis bacteria. In the purple nonsulphur bacterium Rhodospirillum rubrum a soluble c type cytochrome is associated with P870 of the reaction centre. This cytochrome is referred to as cytochrome c₂, and has a high mid point potential of about + 30.0 mV.
Cytochrome c₂ appears to be the electron donor to P870. In PSI of higher plants, plastocyanin (PC), a copper protein, is the electron donor to P700. Algae apparently represent an intermediate stage in evolution, since their electron donor to P700 is a c type cytochrome, although plastocyanin can also be present. Rhodospirillum also contains cytochrome cc' with two different haeme groups.
Purple sulphur bacteria like Chromatium contain cytochrome c₅₅₂ in addition to cytochromes C₂ and cc’. Cytochrome C₅₅₂ (MW 72,000) has two haeme groups and one FMN. The green sulphur bacterium Chlorobium has three cytochromes of the c type, but none of these has the high redox potential of cytochrome, c₂ of purple bacteria and cytochrome f of higher green plants.