title: The redox potentials of the b-type cytochromes of higher plant chloroplasts.
abstract: 1. In fresh chloroplasts,three b-type cytochromes exist. These are b-559HP (lambda max, 559 nm; Em at pH 7, +370 mV; pH-independent Em), b-559LP (lambda max, 559 nm; Em at pH 7, +20 mV; pH-independent Em) and b-563 (lambda max, 563 nm; Em at pH 7, -110 mV; pH-independent Em), b-559HP may be converted to a lower potential form (lambda max, 559 nm; Em at pH 7, +110 mV; pH-independent Em). 2. In catalytically active b-f particle preparations, three cytochromes exist. These are cytochrome f (lambda max, 554 nm; Em at pH 7, +375 mV, pK on oxidised cytochrome at pH 9), b-563 (lambda max, 563 nm; Em at pH 7, -90 mV, small pH-dependence of Em) and a b-559 species (lambda max, 559 nm, Em at pH 7, +85 mV; pH-independent Em). 3. A positive method of demonstration and estimation of b-559LP in fresh chloroplasts is described which involves the use of menadiol as a selective reductant of b-559LP.
mesh_terms: D002736:Chloroplasts / Q000378:metabolism*; D003573:Cytochrome b Group; D003580:Cytochromes / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010944:Plants / Q000378:metabolism; D011199:Potentiometry; D013053:Spectrophotometry
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D010100:Oxygen