title: The kinetics and specificity of electron transfer from cytochromes and copper proteins to P700.
abstract: The rates of electron transfer to P700 from plastocyanin and cytochrome f have been compared with those from three other c-type cytochromes and azurin, a copper protein resembling plastocyanin. Three different disruptive techniques were used to expose P700; digitonin, Triton X-100 and sonication. The following rate constants were measured at 25 degrees C, pH 7.0, with digitonin-treated chloroplasts: plastocyanin, 8 x 10(7)M(-1) x s(-1); red-algal cytochrome c-553, 1.9 x 10(7)M(-1) x s (-1); Pseudomonas cytochrome c-551, 8 x 10(6)M(-1) x s (-1); azurin, less than or = 3 x 10(5)M(-1) x s (-1); cytochrome f, less than or = 2 x 10(4)M(-1) x s (-1); mammalian cytochrome c, less than or = 2 x 10(4)M(-1) x s (-1). For electron transfer from plastocyanin, the effects of ionic strength, pH and temperature were also studied, and saturation effects found in earlier work were avoided by a full consideration of the various secondary reactions and inclusion of superoxide dismutase. The relative rates are discussed in relation to photosynthetic electron transport.
mesh_terms: D001665:Binding Sites; D002736:Chloroplasts / Q000201:enzymology; D003300:Copper; D003580:Cytochromes / Q000378:metabolism*; D004072:Digitonin / Q000494:pharmacology; D004579:Electron Transport; D007700:Kinetics; D008433:Mathematics; D008667:Metalloproteins / Q000378:metabolism*; D010084:Oxidation-Reduction; D010944:Plants; D011092:Polyethylene Glycols / Q000494:pharmacology; D011485:Protein Binding; D011549:Pseudomonas / Q000201:enzymology; D000461:Rhodophyta / Q000201:enzymology; D013010:Sonication
chemical_list: D003580:Cytochromes; D008667:Metalloproteins; D011092:Polyethylene Glycols; D003300:Copper; D004072:Digitonin