PARENT SESSION

Symposium S4Ab Type II reaction centres: acceptor side
Tuesday August 31st, 2004 2:40 PM-4:40 PM Room 510B
Chair: Marilyn Gunner
Co-Chair: Bill Rutherford

Coupling of Light-Induced Electron Transfer to Proton Uptake in Photosynthesis. André Remy^*,1, Klaus Gerwert¹, ¹ Lehrstuhl für Biophysik, Ruhr-Universität Bochum, Postfach 102148, Bochum, Germany

ABSTRACT- Light energy is transformed into chemical energy in photosynthesis by coupling a light-induced electron transfer to proton uptake. The resulting proton gradient drives ATP synthesis. In this study, we monitored the light-induced reactions in a 100-kDa photosynthetic protein from 30 ns to 35 s by FTIR difference spectroscopy. The results provide detailed mechanistic insights into the electron and proton transfer reactions of the Q_A to Q_B transition: Reduction of Q_A in picoseconds induces protonation of histidines, probably of His126 and His128 in the H subunit in the entrance of the proton uptake channel, and of Asp210 in the L subunit insight the channel at 12 micro-s and 150 micro-s. This seems to be a prerequisite for the reduction of Q_B, mainly at 150 micro-s. Q_A^- is reoxidized at 1.1 ms, and a proton is transferred from Asp210 to Glu212 in the L subunit, the proton donor to Q_B^-. Notably, our data indicate that Q_B is not reduced directly by Q_A^-, but presumably through an intermediary electron donor.

KEY WORDS: electron transfer, FTIR spectroscopy, proton uptake, molecular mechanisms