PARENT SESSION
Posters P6A Type II reaction centres: Excited state dynamics and donor side. Abstracts (313-346)

Effects of the steric exclusion of the HB bacteriopheophytin from the Rhodobacter sphaeroides reaction centre. Ashley Watson^*,1, Paul Fyfe¹, Marion Wakeham¹, Eliane Nabedryk², Dmitrij Frolov³, Rienk van Grondelle³, Jacques Breton², Michael Jones¹, ¹ Department of Biochemistry, School of Medical Sciences, Bristol, UK² Service de Bioénergétique, France³ Department of Physics and Astronomy, Amsterdam, The Netherlands

ABSTRACT- The cofactors encased in the Rhodobacter sphaeroides reaction centre are organised into two membrane-spanning branches around an axis of two-fold rotational pseudo-symmetry. The active (A) branch cofactors are involved in electron transfer across the membrane, whilst the symmetrically-organised inactive (B) branch cofactors have other roles. The bacteriochlorophyll at the BB site is thought to play a role in photoprotection, through energy transfer to the reaction centre carotenoid, and the ubiquinone at the QB site is reduced to ubiquinol using electrons delivered from the A-branch. The B-branch HB bacteriopheophytin has no well-defined role, although it has been suggested that it could be involved in light harvesting, photoprotection in response to blue light excitation, or to provide structural symmetry and stability. To investigate the role of this cofactor, site-directed mutations have been made on the L and M polypeptides that either cause replacement of this bacteriopheophytin with a bacteriochlorophyll, or cause steric exclusion of the bacteriopheophytin from the reaction centre. The properties of these mutant complexes will be described.

KEY WORDS: Rhodobacter sphaeroides, cofactors, bacteriopheophytin, reaction centre