Thermodynamical and structural information on photosynthetic systems obtained from electroluminescence kinetics.

The relationship between the thermodynamical and structural properties of photosynthetic reaction centers and kinetics and polarization of electric field-induced luminescence was studied. A general model is presented to describe the influence of an electric field on the individual electron transfer rate constants. Comparison of simulations with this model and experimental curves of Photosystem I electroluminescence showed that (a) at least three electrogenic electron transfer steps occur: P-700 to A(0)( approximately 30%), A(0) to A(1) ( approximately 50%), and A(1) to F(A)( approximately 20%), (b) the midpoint potential of A(1)/A-(1) is approximately - 0.81 V, and (c) the emission moments of the pigments make on average an angle of 67 degrees with the membrane normal. It is concluded that the analysis of electro-luminescence kinetics may be a powerful technique to obtain information on primary processes using relatively intact systems.