Uncoupling of electron and proton transfers in the photocycle of bacterial reaction centers under high light intensity

Biochemistry
László Gerencsér, P Maroti

Abstract

Photosynthetic reaction centers produce and export oxidizing and reducing equivalents in expense of absorbed light energy. The formation of fully reduced quinone (quinol) requires a strict (1:1) stoichiometric ratio between the electrons and H(+) ions entering the protein. The steady-state rates of both transports were measured separately under continuous illumination in the reaction center from the photosynthetic bacterium Rhodobacter sphaeroides. The uptake of the first proton was retarded by different methods and made the rate-limiting reaction in the photocycle. As expected, the rate constant of the observed proton binding remained constant (7 s(-)(1)), but that of the cytochrome photooxidation did show a remarkably large increase from 14 to 136 s(-)(1) upon increase of the exciting light intensity up to 5 W/cm(2) (808 nm) at pH 8.4 in the presence of NiCl(2). This corresponds to about 20:1 (e(-):H(+)) stoichiometric ratio. The observed enhancement is linearly proportional to the light intensity and the rate constant of the proton uptake by the acceptor complex and shows saturation character with quinone availability. For interpretation of the acceleration of cytochrome turnover, an extended model of the photocycle is propo...Continue Reading

References

Aug 1, 1966·Biological Reviews of the Cambridge Philosophical Society·P Mitchell
Jun 6, 2003·FEBS Letters·Carola HunteBernard L Trumpower
Apr 23, 1962·Biochimica Et Biophysica Acta·B van GELDER, E C SLATER
Nov 25, 2003·FEBS Letters·M L PaddockM Y Okamura
Feb 24, 2004·Annual Review of Physiology·Janos K Lanyi

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Citations

Mar 28, 2008·European Biophysics Journal : EBJ·László Gerencsér, Péter Maróti
Jun 27, 2009·Biochimica Et Biophysica Acta·Emese Asztalos, Péter Maróti
Mar 31, 2007·The Journal of Physical Chemistry. B·Francesco MilanoPéter Maróti

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