Dynamics of energy conversion in reaction center core complexes of the green sulfur bacterium Prosthecochloris aestuarii at low temperature.
Excited-state and electron-transfer dynamics at cryogenic temperature in reaction center core (RCC) complexes of the photosynthetic green sulfur bacterium Prosthecochloris aestuarii were studied by means of time-resolved absorption spectroscopy, using selective excitaton of bacteriochlorophyll (BChl) a and of chlorophyll (Chl) a 670. The results indicate that the BChls a of the RCC complex form an excitonically coupled system. Relaxation of the excitation energy within the ensemble of BChl a molecules occurred within 2 ps. A time constant of about 25 ps was ascribed to charge separation. Absorption changes in the 670 nm region, where Chl a 670 absorbs, were fairly complicated. They showed various time constants and were dependent on the wavelength of excitation and they did not lead to a simple picture of the electron acceptor reaction. Energy transfer from Chl a 670 to BChl a occurred with a time constant of 1.5 ps. However, upon excitation of Chl a 670 the amount of oxidized primary electron donor, P840(+), formed relative to that of excited BChl a was considerably larger than upon direct excitation of BChl a. This indicates the existence of an alternative pathway for charge separation which does not involve excited BChl a.
Neerken
S
S
Department of Biophysics, Huygens Laboratory, Leiden University, The Netherlands. sigi@biophys.leidenuniv.nl
Schmidt
K A
KA
Aartsma
T J
TJ
Amesz
J
J
D001429:Bacteriochlorophylls / Q000737:chemistry; D019414:Chlorobi / Q000737:chemistry*; D004579:Electron Transport; D004735:Energy Transfer; D005615:Freezing; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods; D013816:Thermodynamics
D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins