Plasma membrane redox potential

Rieske protain/centar an iron-sulphur protein first isolat from Complex III of the mitochondrial electron transport chain, in which it occurs with cytochromes b and C) [J.S, Rieske el al. Biochem. Biophys Res Commun. IS (1%4) 338-344], but which has now been found in the equivalent cytochrome be complexes in the bacterial plasma membrane and the chloroplast thylakoid membrane. The latter, known as the cytochrome bff complex, partidpates in cyclic and noncyclic electron flow in the light phase of photosynthesis (see Photosynthesis). All Rieske proteins are one-electron redox systems with a standanl redox potential in the + 0.2 to + 0.3V range and have a (2Fe-2S] center, a single membrane-spanning a-helix, and a characteristic electron spin resonance (ESR) spectrum. The chloroplastidic R.p/c, with a M, of - 20,000, is smaller than that of the mitochondnon. It is encoded in the nucleus, synthesized in the cytoplasm and translocated to the chloroplast, where it is inserted into the thylakoid membrane. Within the thylakoid membrane its [2Fe-2S] redox centre (near to its C-terminus) can readily pass electrons to cytochrome /, a c-type cytochrome that projects from the luminal surface cytochrome / then passes electrons to plastocyanin (see) dissolved in the aqueous milieu of the thylakoid lumen. 

Redox reactions are essential for the function of cell membranes (Del Castillo-Olivares et al. 2000). It should be stressed that every bioenergetic-ally competent cell membrane does contain redox systems (Skulackev 1988). A plasma membrane electron transport or redox system has been found in every living cell tested. Voegtlin et al. (1925) examined a relation between the redox state and cancer. The redox potential of cytochrome bsss.. a component of NADPH oxidase, is -245 mV. This is atypically low for a cytochrome b, but this fact enables the reduction of oxygen to snperoxide (Cross... 

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