title: Low-temperature femtosecond-resolution transient absorption spectroscopy of large-scale symmetry mutants of bacterial reaction centers.
abstract: Reaction centers isolated from three large-scale symmetry mutants sym0, sym2-1, and sym5-2 described in the previous article of this issue [Taguchi, A. K. W., Eastman, J. E., Gallo, D. M., Jr., Sheagley, E.. Xiao, W., & Woodbury, N. W. (1996) Biochemistry 35, 3175-3186] have been investigated by low-temperature ground state and ferntosecond-resolution transient absorption spectroscopy. All three of these large-scale symmetry mutants undergo electron transfer at 20 K. The mutants sym0 and sym5-2 have yields and dominant rates of charge separation comparable to wild type. However. the sym2-mutant shows a roughly 35%, quantum yield at this temperature, and the major kinetic component of the initial electron transfer is slower than wild type by nearly a factor of 100. The sym0 mutant showed substantial changes in the monomer bacteriochiorophyll ground state and transient spectra, and both sym0 sym2-1 showed changes in the bacteriopheophyll ground state and transient spectra. In particular, sym2-1 shows a small absorbance decrease in the region of the Qx band of the B side bacteriopheophytin which could be attributed to 10%-20% electron transfer along the B pathway.
authors.affiliation: Department of Chemistry and Biochemistry, Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe 85287-1604, USA.
authors.forename: S
authors.initials: S
authors.lastname: Lin
authors.forename: W
authors.initials: W
authors.lastname: Xiao
authors.forename: J E
authors.initials: JE
authors.lastname: Eastman
authors.forename: A K
authors.initials: AK
authors.lastname: Taguchi
authors.forename: N W
authors.initials: NW
authors.lastname: Woodbury
mesh_terms: D003080:Cold Temperature; D008027:Light; D009154:Mutation; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D016354:Rhodobacter capsulatus / Q000235:genetics*; D013050:Spectrometry, Fluorescence / Q000379:methods; D013053:Spectrophotometry / Q000379:methods; D013329:Structure-Activity Relationship
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins