Inter-and intraspecific variation in excited-state triplet energy transfer rates in reaction centers of photosynthetic bacteria.
In protein-cofactor reaction center (RC) complexes of purple photosynthetic bacteria, the major role of the bound carotenoid (C) is to quench the triplet state formed on the primary electron donor (P) before its sensitization of the excited singlet state of molecular oxygen from its ground triplet state. This triplet energy is transferred from P to C via the bacteriochlorophyll monomer B{sub B}. Using time-resolved electron paramagnetic resonance (TREPR), we have examined the temperature dependence of the rates of this triplet energy transfer reaction in the RC of three wild-type species of purple nonsulfur bacteria. Species-specific differences in the rate of transfer were observed. Wild-type Rhodobacter capsulatus RCs were less efficient at the triplet transfer reaction than Rhodobacter sphaeroides RCs, but were more efficient than Rhodospirillum rubrum RCs. In addition, RCs from three mutant strains of R. capsulatus carrying substitutions of amino acids near P and B{sub B} were examined. Two of the mutant RCs showed decreased triplet transfer rates compared with wild-type RCs, whereas one of the mutant RCs demonstrated a slight increase in triplet transfer rate at low temperatures. The results show that site-specific changes within the RC of R. capsulatus can mimic interspecies differences in the rates of triplet energy transfer. This application of TREPR was instrumental in defining critical energetic and coupling factors that dictate the efficiency of this photoprotective process.
- Research Organization:
- Argonne National Laboratory (ANL)
- Sponsoring Organization:
- SC; LDRD
- DOE Contract Number:
- AC02-06CH11357
- OSTI ID:
- 961121
- Report Number(s):
- ANL/BIO/JA-44770
- Journal Information:
- Photochem. Photobiol., Journal Name: Photochem. Photobiol. Journal Issue: 2 ; Aug. 2003 Vol. 78; ISSN 0031-8655; ISSN PHCBAP
- Country of Publication:
- United States
- Language:
- ENGLISH
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Related Subjects
99 GENERAL AND MISCELLANEOUS
AMINO ACIDS
BACTERIA
BINDING ENERGY
CAROTENOIDS
COMPLEXES
COUPLING
EFFICIENCY
ELECTRON SPIN RESONANCE
ELECTRONS
ENERGY TRANSFER
MONOMERS
MUTANTS
OXYGEN
PHOTOSYNTHETIC BACTERIA
PHOTOSYNTHETIC REACTION CENTERS
RHODOSPIRILLUM
STRAINS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0065-0273 K
TRANSFER REACTIONS
TRIPLETS
VALENCE
VARIATIONS