THE PLANT PLASMA-MEMBRANE B-TYPE CYTOCHROME - AN OVERVIEW

The plasma membrane of higher plants contains a specific b-type cytoch rome. This major component has a high standard redox potential (averag e E'(0) of + 140 mV) and an a-band absorption maximum near 561 nm. Asc orbic acid rapidly reduces the cytochrome but NADH or NADPH are ineffe ctive as a reductant. The redox protein has been detected in purified plasma membranes of a variety of plant species and tissues and it appe ars to be a common plasma membrane component. Specific concentrations range from 20 to 400 pmol per mg protein. Initial attempts to purify t he protein indicated a molecular weight of 31 kDa and suggest that the cytochrome may be a glycoprotein. The current hypotheses on the physi ological importance of the plant plasma membrane cytochrome are focuse d on ascorbate-mediated transmembrane electron transport and blue ligh t photoperception.