Re-examination of primary radical pair recombination in Rp. viridis with QA reduced

Charge recombination in the primary radical pair P⁺H⁻ of the purple photosynthetic bacterium Rp. viridis with pre-reduced secondary acceptor Q_A, has been studied by time-resolved photovoltage measurements and transient absorption spectroscopy with a time resolution of 1 ns. The lifetime of P⁺H⁻ was found to be 2.4–3 ns in intact membranes and ∼5 ns in isolated reaction centers, in contrast to a lifetime of ∼15 ns which has been widely accepted in the literature for reaction centers. The origin of the difference between lifetimes of P⁺H⁻ in membranes and isolated reaction centers is discussed.