Quantum Yield for the Photoproduced Electron Paramagnetic Resonance Signal in Chromatophores from Rhodospirillum rubrum

A 1:1 correspondence has been demonstrated between the concentrations of photoproduced spins in chromatophores of Rhodospirillum rubrum, as measured by electron paramagnetic resonance techniques, and the concentration of the reaction center primary electron donor molecule (P₃₇₀ or P_0.44), as measured by absorbance change at 865 nm. In addition a significantly high quantum yield (0.8 with 880-nm light) has been determined for the electron paramagnetic resonance signal production. When all existing data relating to the photoproduced absorbance change at 865 nm and the photoproduced electron paramagnetic resonance signal are reviewed, together with these results, the conclusion seems inescapable that these are two properties reflecting change in oxidation state of a single molecular species.