Light-Induced Equilibration Kinetics in Membrane-Bound Photosynthetic Reaction Centers: Nonlinear Dynamic Effects in Multiple Scattering Media

Abstract

Nonequilibrium dynamic effects in membrane-bound reaction centers (RCs) from photosynthetic bacteria are studied for the first time. We show that the accumulation of slow conformational changes triggered by charge-separation events in the RCs control system dynamics and depend on illumination conditions in a way similar to that for isolated RCs. The light-induced, transient kinetics of membrane-bound RCs are described using a model of electron-conformational transitions governed by system diffusion along the surface of a double-well, effective adiabatic potential. The light-triggered conformational transitions in the chromatophores are estimated to occur at an actinic light intensity at least 10 times lower than that needed for conformational transitions in isolated RCs. This finding is attributed to efficient, multiple-scattering effects that occur in sample with membranes. Related optical properties of the chromatophores as a disordered system with multiple light scattering are characterized for the first time.