title: Manipulating the direction of electron transfer in the bacterial reaction center by swapping Phe for Tyr near BChl(M) (L181) and Tyr for Phe near BChl(L) (M208).
abstract: We have investigated the primary charge separation processes in Rb. capsulatus reaction centers (RCs) bearing the mutations Phe(L181) --> Tyr, Tyr(M208) --> Phe, and Leu(M212) --> His. In the YFH mutant, decay of the excited primary electron donor P occurs with an 11 +/- 2 ps time constant and is trifurcated to give (1) internal conversion to the ground state ( approximately 10% yield), (2) charge separation to the L side of the RC ( approximately 60% yield), and (3) electron transfer to the M-side bacteriopheophytin BPh(M) ( approximately 30% yield). These results relate previous work in which the ionizable residues Lys (at L178) and Asp (at M201) have been used to facilitate charge separation to the M side of the RC, and the widely studied L181 and M208 mutants. One conclusion that comes from this work is that the Tyr (M208) --> Phe and Gly(M201) --> Asp mutations near the L-side bacteriochlorophyll (BChl(L)) raise the free energy of P(+)BChl(L)(-) by comparable amounts. The results also suggest that the free energy of P(+)BChl(M)(-) is lowered more substantially by a Tyr at L181 than a Lys at L178. The results on the YFH mutant further demonstrate that the free energy differences between the L- and M-side charge-separated states play a significant role in the directionality of charge separation in the wild-type RC, and place limits on the contributing role of differential electronic matrix elements on the two sides of the RC.
authors.affiliation: Department of Chemistry, Washington University, St. Louis, Missouri 63130, USA. kirmaier@wuchem.wustl.edu
authors.forename: C
authors.initials: C
authors.lastname: Kirmaier
authors.forename: C
authors.initials: C
authors.lastname: He
authors.forename: D
authors.initials: D
authors.lastname: Holten
mesh_terms: D004579:Electron Transport; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D009154:Mutation; D010649:Phenylalanine / Q000737:chemistry; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics; D016354:Rhodobacter capsulatus / Q000737:chemistry; D014443:Tyrosine / Q000737:chemistry
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D014443:Tyrosine; D010649:Phenylalanine