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

Redox potentials of quinones controlled by hydrogen bonding pattern in photosystem II. Hiroshi Ishikita^*,1, Ernst-Walter Knapp¹, ¹ Free University of Berlin, Institute of Chemistry, Takustrasse 6, Berlin, Germany

ABSTRACT- Based on the most recent crystal structures of the photosystem II (PSII) membrane protein complex at 3.5 resolution ¹ we performed electrostatic energy computations to elucidate the energetics of the cofactor redox states in PSII involved in electron transfer (ET) processes. The electrostatic energy computations are based on the solution of the Poisson Boltzmann equation that accounts for heterogeneous dielectric, which is low inside the protein and high in the solvent. Inside the protein an explicit charge distribution based on a suitable choice of atomic partial charges is used. The statistical distribution of charge patterns of variably charged molecular groups (titratable and redox-active) is sampled by a Monte Carlo method (Karlsberg: online manual, http://agknapp.chemie.fu-berlin.de/karlsberg/).
We found that the calculated redox potentials of quinones in PSII as well as those in bacterial photosynthetic reaction center (bRC) ² are controlled by the H-bonding pattern with quinones. The further features will be discussed in comparison with those in bRC ^2,3 or PSI ⁴.


1. Ferreira, K. N., Iverson, T. M., Maghlaoui, K., Barber, J., and Iwata, S. (2004) Science 303, 1831-1838.
2. Ishikita, H. and Knapp, E. W. (2004) J. Am. Chem. Soc. in press.
3. Ishikita, H., Morra, G. and Knapp, E. W. (2003) Biochemistry 42, 3882-3892.
4. Ishikita, H. and Knapp, E. W. (2003) J. Biol. Chem. 278, 52002-52011.

KEY WORDS: electron transfer & proton transfer, reaction center & photosystem, quinone redox potential computation, hydrogen bond & protonation