Partial equilibrium of photosynthetic electron carriers under weak illumination: a theoretical and experimental study
1989
Lavergne, J. | Joliot, P. | Vermeglio, A.
When submitting photosynthetic material to weak illumination, in uncoupled conditions, quasi-equilibrium states of the redox carriers are attained that should presumably reflect the equilibrium constants deduced from the mid-point potentials. However, the apparent constants experimentally obtained are, in several instances, much lower than expected. In order to account for such discrepancies, we examine the consequences of 'clustering' of neighboring carriers, assuming rapid equilibration within a cluster, but much slower relaxation towards the intercluster equilibrium. A general treatment is developed and its predictive content is discussed. Its application to two experimental systems is described, namely the donor chain of isolated reaction centers of Rhodopseudomonas viridis, and the donor chain of Rhodobacter sphaeroides in vivo, investigated in the accompanying paper (Joliot, P., Vermeglio, A. and A. Joliot) (1989) Biochim. Biophys. Acta 975, 336-346). Possible extension of this class of hypothesis to the donor chain of Photosystem I and to the acceptor chain of Photosystem II in chloroplasts is suggested.
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