Absence of large-scale displacement of quinone QB in bacterial photosynthetic reaction centers |
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Authors: | Breton Jacques |
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Affiliation: | Service de Bioénergétique, Bat. 532, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France. cadara3@dsvidf.cea.fr |
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Abstract: | Photosynthesis transforms light into chemical energy by coupling electron transfer to proton uptake at the quinone Q(B). The possibility of initiating this process with a brief pulse of light and the known X-ray structure makes the photosynthetic bacterial reaction center a paradigm for studying coupled electron-proton transfer in biology. It has been established that electron transfer from the primary quinone Q(A) to Q(B) is gated by a protein conformational change. On the basis of a dramatic difference in the location of Q(B) in structures derived from crystals cooled to 90 K either under illumination or in the dark, a functional model for the gating mechanism was proposed whereby neutral Q(B) moves 4.5 A before receiving the electron from Q(A)(-) [Stowell, M. H. B., McPhillips, T. M., Rees, D. C., Soltis, S. M., Abresch, E., and Feher, G. (1997) Science 276, 812-816]. Isotope-edited FTIR difference spectroscopy of Q(B) photoreduction at 290 and 85 K is used to investigate whether Q(B) moves upon reduction. We show that the specific interactions of the carbonyl groups of Q(B) and Q(B)(-) with the protein at a single binding site remain identical at both temperatures. Therefore, the different locations of Q(B) reported in many X-ray crystal structures probably are unrelated to functional electron transfer from Q(A)(-) to Q(B). |
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