PARENT SESSION
Posters P3A Bacteriochlorophyll based antenna systems. Abstracts (219-238)

Investigation of B-side electron transfer in multiple mutant reaction centre from Rb. Sphaeroides by femtosecond time resolved spectroscopy. Dmitrij Frolov^*,1, Marion Wakeham², Elena Andrizhiyevskaya¹, Michael Jones², Rienk van Grondelle¹, ¹ Vrije Universiteit, Amsterdam, The Netherlands² University of Bristol, Bristol, United Kingdom

ABSTRACT-  In photosynthetic organisms, conversion of solar energy into chemical potential energy is mediated by integral membrane pigment protein complexes named reaction centres. In reaction centres of photosynthetic purple bacteria, this energy conversion involves the reduction of a quinone molecule on the cytoplasmic side of the photosynthetic membrane and the oxidation of a cytochrome at the periplasmic surface [1]. As known from X-ray crystallographic studies [2-4], the purple bacterial reaction centre consist of three polypeptides, L and M and H, as well as none-heme iron atom and four bacteriochlorophylls, two bacteriopheophytins, one carotenoid and two quinones.Despite the remarkably symmetric organization of the cofactors along the C2 axis, the electron transfer in bacterial reaction centres is highly asymmetric, as it essentially occurs along the set of cofactors which is more closely associated with the L subunit [5]. The probability for an electron to follow the L-branch pathway is thought to be at least two orders of magnitude higher than for the M branch [6-7]. In our work, the electrons transfer dynamics in bacterial reaction centres mutant from Rb. Sphaeroides designed to study electron transfer via inactive branch was investigated by means of femtosecond transient absorption spectroscopy. LM214H mutation that leads to exchange of native bacteriopheophytin to the bacteriochlorophyll along active branch as well as AM260W mutation that leads to lose of primary quinone (Qa) and EL212A/DL213A mutations in Qb pocket results in 8% yield of P+Qb- state formation after excitation at 795 nm.  References: 1. Hoff, A. J.; Deisenhofer, J. Physics Reports, 1997, 287, 1-247. 2. Deisenhofer, J.; Epp, O.; Miki, K.; Huber, R.; Michel, H. J. Mol. Biol., 1984, 180, 385-398. 3. Deisenhofer, J.; Epp, O.; Sinning, I.; Michel, H. Nature, 1985, 318, 618-624. 4. Allen, J. P.; Feher, G.; Yeates, T. O.; Rees, D. C.; Deisenhofer, J.; Michel, H.; Huber, R. Proc. Natl. Acad. Sci. U.S.A., 1986, 83, 8589-8593. 5. Kirmaier, C.; Holten, D.; Parson, W.W. Biochim. Biophys. Acta, 1985, 810, 49-61. 6. Kellogg, E.C.; Kolacskowski, S.; Wasielewski, M.R.; Tiede, W., Photosynth. Res.,1989, 22, 47-59 7. Gunner, M. R.; Nicholls, A.; Honig, B. J. Phys. Chem., 1996, 100, 4277-4291

KEY WORDS: electron transfer, bacterial reaction centres