The Binding and Interaction of Pigments and Quinones in Bacterial Reaction Centers Studied by Infrared Spectroscopy

Abstract

The primary photochemistry in bacterial photosynthesis involves a charge separation, stable for milliseconds to seconds, between specialized pigments acting as the primary electron donor and the intermediary electron acceptor, and quinones acting as primary and secondary electron acceptors. In bacterial reaction centers, the primary electron donor (P) is a bacteriochlorophyll (BChl) a or b dimer, the intermediary acceptor (H) is a bacteriopheophytin (BPheo) a or b monomer, and ubiquinones or menaquinones have been identified as electron acceptors (Q). The specifity, efficiency and stability of this charge separation relies on the arrangement and specific interaction of the pigments and redox components in the protein matrix. X-ray structures available for bacterial RC [1,2] provide a static picture of the quiescent state and suggest specific interactions of the pigments and quinones with their host site. However, additional information on the mechanisms and dynamics of primary electron transfer and on the concomitant change of interactions and protein conformation is required. Time-resolved optical spectroscopy (for a review, see [3]) as well as resonance Raman spectroscopy (for a review, see [4]) have provided such information.