Proton Uptake of Rhodobacter capsulatus Reaction Center Mutants Modified in the Primary Quinone Environment¶†

Flash-induced absorbance spectroscopy was used to an-alyze the proton uptake and electron transfer properties of photosynthetic reaction centers (RC) of Rhodobacter capsulatus that have been genetically modified near the primary quinone electron acceptor (QA). M246Ala and M247Ala, which are symmetry-related to the positions of two acidic groups, L212Glu and L213Asp, in the second-ary quinone electron acceptor (QB) protein environment, have been mutated to Glu and Asp, respectively. The pH dependence of the stoichiometry of proton uptake upon formation of the P1QA2 (H1/P1QA2) and PQA2 (H1/QA2) (P is the primary electron donor, a noncovalently linked bacteriochlorophyll dimer) states have been measured in the M246Ala → Glu and the M247Ala → Asp mutan