Charge separation in a reaction center incorporating bacteriochlorophyll for photoactive bacteriopheophytin.
Site-directed mutagenic replacement of M subunit Leu214 by His in the photosynthetic reaction center (RC) from Rhodobacter sphaeroides results in incorporation of a bacteriochlorophyll molecule (BChl) in place of the native bacteriopheophytin (BPh) electron acceptor. Evidence supporting this conclusion includes the ground-state absorption spectrum of the (M)L214H mutant, pigment and metal analyses, and time-resolved optical experiments. The genetically modified RC supports transmembrane charge separation from the photoexcited BChl dimer to the primary quinone through the new BChl molecule, but with a reduced quantum yield of 60 percent (compared to 100 percent in wild-type RCs). These results have important implications for the mechanism of charge separation in the RC, and rationalize the choice of (bacterio)pheophytins as electron acceptors in a variety of photosynthetic systems.
Kirmaier
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Department of Chemistry, Washington University St. Louis, MO 63130.
Gaul
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DeBey
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Holten
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Schenck
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D001429:Bacteriochlorophylls / Q000378:metabolism*; D004579:Electron Transport; D006639:Histidine; D007700:Kinetics; D007930:Leucine; D045342:Light-Harvesting Protein Complexes; D016297:Mutagenesis, Site-Directed; D010674:Pheophytins / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D013053:Spectrophotometry
D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D010674:Pheophytins; D045322:Photosynthetic Reaction Center Complex Proteins; C006678:bacteriopheophytin; D006639:Histidine; D007930:Leucine