Inter-and intraspecific variation in excited-state triplet energy transfer rates in reaction centers of photosynthetic bacteria.

Journal Article · Fri Aug 01 00:00:00 EDT 2003 · Photochem. Photobiol.

DOI:https://doi.org/10.1562/0031-8655(2003)078<0114:IAIVIE>2.0.CO;2· OSTI ID:961121

Laible, P D; Morris, Z S; Thurnauer, M C; Schiffer, M; Hanson, D K

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 Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC); USDOE Laboratory Directed Research and Development (LDRD) Program
• DOE Contract Number: DE-AC02-06CH11357
• OSTI ID: 961121
• Report Number(s): ANL/BIO/JA-44770; PHCBAP; TRN: US201010%%947
• Journal Information: Photochem. Photobiol., Vol. 78, Issue 2 ; Aug. 2003; ISSN 0031-8655
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
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