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

Formation of a ubiquinone anion via B-branch electron transfer in the reaction centre from Rhodobacter sphaeroides.. Marion Wakeham ¹, Eliane Nabedryk², Dmitrij Frolov³, Bruno Robert⁴, Jane Potter¹, Rienk van Grondelle³, Jacques Breton², Michael Jones^*,1, ¹ Department of Biochemistry, School of Medical Sciences, Bristol, United Kingdom² Service de Bioénergétique, France³ Department of Physics and Astronomy, Amsterdam, The Netherlands⁴ Section de Biophysique des Fonctions Membranaires, France

ABSTRACT- In Rhodobacter sphaeroides reaction centers (RCs) containing the mutation Ala M260 to Trp (AM260W), transmembrane electron transfer along the full length of the A-branch of cofactors is prevented by the loss of the Q_A ubiquinone, but it is possible to generate the radical pair P⁺H_A^- by A-branch electron transfer or the radical pair P⁺Q_B^- by B-branch electron transfer. The present study examines the spectroscopic properties of the Q_Bubiquinone anion produced by B-branch electron transfer, and compares them with those of the ubiquinone anion produced by A-branch electron transfer. Results from FTIR difference spectroscopy give insights into the binding position of the Q_B ubiquinone anion at both room temperature and 100 K. Factors that affect the yield of B-branch electron transfer are discussed, including the structural effects of mutations as determined by X-ray crystallography and a range of spectroscopic techniques. This work is also co-authored by Dr Paul K. Fyfe and Carolyn Doughty, Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, United Kingdom

KEY WORDS: reaction centre, electron transfer, Rhodobacter sphaeroides, B-branch