Electronic structure of the primary electron donor of Blastochloris viridis heterodimer mutants : high field EPR study.

Journal Article · Wed Sep 01 00:00:00 EDT 2010 · Biochim. Biophys. Acta - Bioenergetics

DOI:https://doi.org/10.1016/j.bbabio.2010.06.002· OSTI ID:993390

Ponomarenko, N S; Poluektov, O G; Bylina, E J; Norris, J R

High-field electron paramagnetic resonance (HF EPR) has been employed to investigate the primary electron donor electronic structure of Blastochloris viridis heterodimer mutant reaction centers (RCs). In these mutants the amino acid substitution His(M200)Leu or His(L173)Leu eliminates a ligand to the primary electron donor, resulting in the loss of a magnesium in one of the constituent bacteriochlorophylls (BChl). Thus, the native BChl/BChl homodimer primary donor is converted into a BChl/bacteriopheophytin (BPhe) heterodimer. The heterodimer primary donor radical in chemically oxidized RCs exhibits a broadened EPR line indicating a highly asymmetric distribution of the unpaired electron over both dimer constituents. Observed triplet state EPR signals confirm localization of the excitation on the BChl half of the heterodimer primary donor. Theoretical simulation of the triplet EPR lineshapes clearly shows that, in the case of mutants, triplet states are formed by an intersystem crossing mechanism in contrast to the radical pair mechanism in wild type RCs. Photooxidation of the mutant RCs results in formation of a BPhe anion radical within the heterodimer pair. The accumulation of an intradimer BPhe anion is caused by the substantial loss of interaction between constituents of the heterodimer primary donor along with an increase in the reduction potential of the heterodimer primary donor D/D{sup +} couple. This allows oxidation of the cytochrome even at cryogenic temperatures and reduction of each constituent of the heterodimer primary donor individually. Despite a low yield of primary donor radicals, the enhancement of the semiquinone-iron pair EPR signals in these mutants indicates the presence of kinetically viable electron donors.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC02-06CH11357
• OSTI ID: 993390
• Report Number(s): ANL/CSE/JA-67279; TRN: US201023%%322
• Journal Information: Biochim. Biophys. Acta - Bioenergetics, Vol. 1797, Issue 8 ; Sep. 2010
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
AMINO ACIDS
ANIONS
BINDING ENERGY
CRYOGENICS
CYTOCHROMES
DIMERS
DISTRIBUTION
ELECTRON SPIN RESONANCE
ELECTRONIC STRUCTURE
ELECTRONS
EXCITATION
MAGNESIUM
MUTANTS
OXIDATION
RADICALS
SIMULATION
TRIPLETS
VALENCE