Inhibition and labelling of isolated reaction centers from Rhodobacter sphaeroides by dicyclohexylcarbodiimide |
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Authors: | David R. Paterson Colin A. Wraight |
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Affiliation: | (1) Department of Plant Biology, University of Illinois at Urbana-Champaign, 61801 Urbana, IL, USA;(2) Department of Physiology and Biophysics, University of Illinois at Urbana-Champaign, 61801 Urbana, IL, USA;(3) Present address: Department of Molecular Biology, University of Chicago, 60637 Chicago, IL, USA;(4) Department of Plant Biology, University of Illinois, 505, S. Goodwin Ave, 61801 Urbana, IL, USA |
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Abstract: | The effect of dicyclohexylcarbodiimide (DCCD) on electron transfer in the acceptor quinone complex of reaction centers (RC) from Rhodobacter sphaeroides is reported. DCCD covalently labelled the RC over a wide concentration range. At low concentrations (<10 M) the binding was specific for the L subunit. At relatively high concentrations (>100 M) DCCD accelerated the rate of charge recombination of the P+QB- state, consistent with a decrease in the equilibrium constant between QA-QB and QAQB-. At similar concentrations, in the presence of cytochrome c as exogenous donor, turnover of the RC was inhibited such that only three cytochromes were oxidized in a train of flashes. Both these inhibitory effects were fully reversed by dialysis, indicating that stable covalent binding was not involved. Possible mechanisms of action are discussed in terms of the putative role of specific residues in proton transfer and protonation and release of quinol from the RC. |
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Keywords: | Photosynthesis reaction centers quinones dicyclohexylcarbodiimide Rb. sphaeroides |
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