Thermodynamic properties of the reaction center of Rhodopseudomonas viridis. In vivo measurement of the reaction center bacteriochlorophyll-primary acceptor intermediary electron carrier.

The thermodynamic properties of redox components associated with the reaction center of Rhodopseudomonas viridis have been characterized with respect to their midpoint potentials and relationship with protons. In particular a midpoint potential for the intermediary electron carrier acting between the reaction center bacteriochlorophyll and the primary acceptor has been determined. The rationale for this measurement was that the light-induced triplet/biradical EPR signal would not be observed if this intermediate was chemically reduced before activation. The midpoint potential of the intermediary at pH 10.8 is about --400 mV (n=1).