Proton transfer in the photosynthetic reaction center of Blastochloris viridis

Photosynthetic reaction centers of Blastochloris viridis require two quanta of light to catalyse a two-step reduction of their secondary ubiquinone Q(B) to ubiquinol. We employed capacitive potentiometry to follow the voltage changes that were caused by the accompanying transmembrane proton displacements. At pH 7.5 and 20 degrees C, the Q(B)-related voltage generation after the first flash was contributed by a fast, temperature-independent component with a time constant of similar to 30 mu s and a slower component of similar to 200 mu s with activation energy (E-a) of 50 kJ/mol. The kinetics after the second flash featured temperature-independent components of 5 ps and 200 ps followed by a component of 600 ps with E-a similar to 60 kJ/mol. (C) 2007 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.