Primary charge separation routes in the BChl:BPhe heterodimer reaction centers of Rhodobacter sphaeroides.
Energy transfer and the primary charge separation process are studied as a function of excitation wavelength in membrane-bound reaction centers of Rhodobacter sphaeroides in which the excitonically coupled bacteriochlorophyll homodimer is converted to a bacteriochlorophyll-bacteriopheophytin heterodimer, denoted D [Bylina, E. J., and Youvan, D. C. (1988) Proc. Natl. Acad. Sci. U.S. A. 85, 7226]. In the HM202L heterodimer reaction center, excitation of D using 880 nm excitation light results in a 43 ps decay of the excited heterodimer, D. The decay of D results for about 30% in the formation of the charge separated state D+QA- and for about 70% in a decay directly to the ground state. Upon excitation of the monomeric bacteriochlorophylls using 798 nm excitation light, approximately 60% of the excitation energy is transferred downhill to D, forming D. Clear evidence is obtained that the other 40% of the excitations results in the formation of D+QA- via the pathway BA --> BA+HA- --> D+HA- --> D+QA-. In the membrane-bound "reversed" heterodimer reaction center HL173L, the simplest interpretation of the transient absorption spectra following B excitation is that charge separation occurs solely via the slow D-driven route. However, since a bleach at 812 nm is associated with the spectrum of D in the HL173L reaction center, it cannot be excluded that a state including BB is involved in the charge separation process in this complex.
van Brederode
M E
ME
Faculty of Sciences, Division of Physics and Astronomy, Department of Biophysics, Vrije Universiteit, Amsterdam, The Netherlands.
van Stokkum
I H
IH
Katilius
E
E
van Mourik
F
F
Jones
M R
MR
van Grondelle
R
R
D001429:Bacteriochlorophylls / Q000737:chemistry* / Q000378:metabolism; D019281:Dimerization; D004735:Energy Transfer; D007700:Kinetics; D007930:Leucine / Q000235:genetics; D045342:Light-Harvesting Protein Complexes; D008715:Methionine / Q000235:genetics; D008956:Models, Chemical; D016297:Mutagenesis, Site-Directed; D010674:Pheophytins / Q000737:chemistry* / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000737:chemistry* / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013696:Temperature; D014451:Ubiquinone / Q000378:metabolism
D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D010674:Pheophytins; D045322:Photosynthetic Reaction Center Complex Proteins; D014451:Ubiquinone; C006678:bacteriopheophytin; D008715:Methionine; D007930:Leucine