title: Proton release upon oxidation of tyrosine in reaction centers from Rhodobacter sphaeroides.
abstract: Markedly different light-induced protonational changes were measured in two reaction center mutants of Rhodobacter sphaeroides. A quadruple mutant containing alterations, at residues L131, M160, M197, and M210, that elevate the midpoint potential of the bacteriochlorophyll dimer was compared to the Y(M) mutant, which contains these alterations plus a tyrosine at M164 serving as a secondary electron donor [Kálmán et al., Nature 402 (1999) 696]. In the quadruple mutant, a proton uptake of 0.1-0.3 H(+)/reaction center between pH 6 and 10 resulted from formation of the oxidized bacteriochlorophyll donor and reduced primary quinone. In the Y(M) mutant, a maximal proton release of -0.5 H(+)/reaction center at pH 8 was attributed to formation of the tyrosyl radical and modeled using electrostatic and direct proton-releasing mechanisms.
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287-1604, USA.
authors.forename: L
authors.initials: L
authors.lastname: Kálmán
authors.forename: J C
authors.initials: JC
authors.lastname: Williams
authors.forename: J P
authors.initials: JP
authors.lastname: Allen
mesh_terms: D019943:Amino Acid Substitution; D001429:Bacteriochlorophylls / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D017354:Point Mutation; D011487:Protein Conformation; D011522:Protons; D012242:Rhodobacter sphaeroides / Q000235:genetics / Q000378:metabolism*; D055672:Static Electricity; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D011522:Protons; D014443:Tyrosine