Cytochrome c and c2 binding dynamics and electron transfer with photosynthetic reaction center protein and other integral membrane redox proteins.
To further the understanding of the details of c-type cytochrome action as a redox carrier between major electron-transfer proteins, the single-turnover kinetics time course of cytochrome c and cytochrome c2 oxidation by flash-activated photosynthetic reaction center (purified from the bacterium Rhodobacter sphaeroides) has been examined under a wide variety of conditions of concentration, ionic strength, and viscosity with reaction center present in detergent dispersion and phosphatidylcholine proteoliposomes. We find that the three-state model proposed by Overfield and Wraight [Overfield, R. E., & Wraight, C. A. (1980) Biochemistry 19, 3322-3327] is generally sufficient to model the kinetics time course; many similarities are found with the cytochrome c-cytochrome c oxidase interaction in mitochondria. Further, we find the following: (1) Significant "product inhibition" by oxidized cytochrome c (c2) bound to the reaction center is apparent. (2) The viscosity sensitivity of the electron transfer into the reaction center from bound cytochrome c (c2) suggests a physical interpretation of the distal state. (3) The exchange dynamics of oxidized and reduced cytochrome c (c2) are similar regardless of the state of activation of the reaction center. (4) Preferential binding of the oxidized form of cytochrome c is revealed upon reconstitution of the reaction center into neutral lipid vesicles, permitting an independent confirmation of the binding suggested by the kinetics. (5) Flash-activated electron-transfer kinetics in reaction center hybrid protein systems have shown that diffusion and competitive binding characterize the behavior of cytochrome c as a redox carrier between the reaction center protein and either the cytochrome bc1 complex or the cytochrome c oxidase.
Moser
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CC
Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia 19104.
Dutton
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PL
D001426:Bacterial Proteins / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism*; D045362:Cytochromes c2; D007700:Kinetics; D008027:Light; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins; D012242:Rhodobacter sphaeroides / Q000378:metabolism*
D001426:Bacterial Proteins; D003574:Cytochrome c Group; D045322:Photosynthetic Reaction Center Complex Proteins; D045362:Cytochromes c2