ESR and ENDOR of bacteriopheophytin a radicals. Implications for bacteriochlorophylls in vivo
The model studies presented here seek to probe effects that the protein environment may induce or impose on the conformation and electronic configuration of photosynthetic chromophores. The cation radicals observed on photooxidation of bacterial reaction centers have been assigned previously to dimeric bacteriochlorophylls (BChl) a or b on the basis of comparisons of ESR and ENDOR characteristics in vivo with those observed for BChl/sup +/ a and b in vitro. Recent X-ray results of the Rhodopseudomonas viridis reaction center (BChl b) support the dimer formulation for its unoxidized primary donor, P960, and provide evidence of possible interactions between the magnesium and the oxygen of a nearby 2-acetyl group, as well as of ligation by neighboring protein residues. Chlorophylls further interact with their environment by hydrogen bonding of their peripheral carbonyl groups, as evidenced by resonance Raman data. To separate ligation and/or hydrogen bonding effects from the intrinsic unpaired spin distributions of BChl radicals, the ENDOR parameters of the cation radical of bacteriopheophytin a (BPheo, a demetalated BChl) have been measured as a function of solvent and temperature. 19 references, 2 figures, 1 table.
- Research Organization:
- Brookhaven National Lab., Upton, NY
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 5820063
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 108:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
PHYTOCHROMES
CONFORMATIONAL CHANGES
ELECTRONIC STRUCTURE
CHEMICAL BONDS
ELECTRON SPIN RESONANCE
ENDOR
EXPERIMENTAL DATA
HYDROGEN
IN VIVO
LIGANDS
PHOTOSYNTHESIS
PROTEINS
RADICALS
SOLVENTS
TEMPERATURE DEPENDENCE
CHEMICAL REACTIONS
DATA
ELEMENTS
INFORMATION
MAGNETIC RESONANCE
NONMETALS
NUMERICAL DATA
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
PIGMENTS
RESONANCE
SYNTHESIS
550200* - Biochemistry