title: Kinetics of flash-induced electron transfer between bacterial reaction centres, mitochondrial ubiquinol:cytochrome c oxidoreductase and cytochrome c.
abstract: Ascorbate-reduced horse heart cytochrome c reduces photo-oxidized bacterial reaction centres with a second-order rate constant of (5-8) X 10(8) M-1 X s-1 at an ionic strength of 50 mM. In the absence of cytochrome c, the cytochrome c1 in the ubiquinol:cytochrome c oxidoreductase is oxidized relatively slowly (k = 3.3 X 10(5) M-1 X s-1). Ferrocytochrome c binds specifically to ascorbate-reduced reductase, with a Kd of 0.6 microM, and only the free cytochrome c molecules are involved in the rapid reduction of photo-oxidized reaction centres. The electron transfer between ferricytochrome c and ferrocytochrome c1 of the reductase is rapid, with a second-order rate constant of 2.1 X 10(8) M-1 X s-1 at an ionic strength of 50 mM. The rate of electron transfer from the Rieske iron-sulphur cluster to cytochrome c1 is even more rapid. The cytochrome b of the ubiquinol:cytochrome c oxidoreductase can be reduced by electrons from the reaction centres through two pathways: one is sensitive to antimycin and the other to myxothiazol. The amount of cytochrome b reduced in the absence of antimycin is dependent on the redox potential of the system, but in no case tested did it exceed 25% of the amount of photo-oxidized reaction centres.
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism*; D002417:Cattle; D003574:Cytochrome c Group / Q000378:metabolism*; D014450:Electron Transport Complex III; D006736:Horses; D007700:Kinetics; D008929:Mitochondria, Heart / Q000201:enzymology*; D009097:Multienzyme Complexes / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D010084:Oxidation-Reduction; D010782:Photolysis; D045322:Photosynthetic Reaction Center Complex Proteins; D011808:Quinone Reductases / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D003574:Cytochrome c Group; D009097:Multienzyme Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D009247:NADH, NADPH Oxidoreductases; D011808:Quinone Reductases; D014450:Electron Transport Complex III