Reconstitution of Photochemical Activity in Rhodobacter capsulatus Reaction Centers Containing Mutations at Tryptophan M-250 in the Primary Quinone Binding Site
Tryptophan M-250 (TrpM250) in the reaction center (RC) of the purple non-sulfur bacteria occupies a key position between the photoactive pheophytin (HA) and the primary quinone (QA), according to the X-ray crystal structures obtained for Rps. viridis and Rb. sphaeroides (refs. 1,2; Fig. 1). Seven directed mutations have been introduced at this position in a related organism, Rb. capsulatus, in order to determine their effects on quinone binding and electron transfer (for a review, see ref.3). The results of these substitutions indicate that although TrpM250 is important for high-affinity quinone binding, primary photochemistry can be reconstituted in all of the genetically modified RCs by addition of exogenous quinone.
KeywordsPhotochemical Activity Primary Photochemistry Photosynthetic Growth Quinone Binding Indole Side Chain
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