EPR characterization of genetically modified reaction centers of Rhodobacter capsulatus

Journal Article · Tue Jul 03 04:00:00 EDT 1990 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00478a013· OSTI ID:6273143

Bylina, E J; Kolaczkowski, S V; Norris, J R; Youvan, D C ^[1]

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1. Massachusetts Institute of Technology, Cambridge (USA)

Electron paramagnetic resonance (EPR) has been used to investigate the cation and triplet states of Rhodobacter capsulatus reaction centers (RCs) containing amino acid substitutions affecting the primary donor, monomeric bacteriochlorophylls (Bchls), and the photoactive bacteriopheophytin (Bphe). The broadened line width of the cation radical in HisM200----Leu and HisM200----Phe reaction centers, whose primary donor consists of a Bchl-Bphe heterodimer, indicates a highly asymmetric distribution of the unpaired electron over the heterodimer. A T0 polarized triplet state with reduced yield is observed in heterodimer-containing RCs. The zero field splitting parameters indicate that this triplet essentially resides on the Bchl half of the heterodimer. The cation and triplet states of reaction centers containing HisM200----Gln, HisL173----Gln, GluL104----Gln, or GluL104----Leu substitutions are similar to those observed in wild type. Oligonucleotide-mediated mutagenesis has been used to change the histidine residues that are positioned near the central Mg2+ ions of the reaction center monomeric bacteriochlorophylls. Reaction centers containing serine substitutions at M180 and L153 or a threonine substitution at L153 have unaltered pigment compositions and are photochemically active. The cation and triplet states of HisL153----Leu reaction centers are similar to those observed in wild type. Triplet energy transfer to carotenoid is not observed at 100 K in HisM180----Arg chromatophores. These results have important implications for the structural requirements of tetrapyrrole binding and for our understanding of the mechanisms of primary electron transfer in the reaction center.

• OSTI ID: 6273143
• Journal Information: Biochemistry; (USA), Journal Name: Biochemistry; (USA) Vol. 29:26; ISSN 0006-2960; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140505 -- Solar Energy Conversion-- Photochemical
Photobiological
& Thermochemical Conversion-- (1980-)
550200* -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
AMINO ACID SEQUENCE
CATIONS
CHARGED PARTICLES
CHEMICAL REACTIONS
CHLOROPHYLL-BINDING PROTEINS
ELECTRON SPIN RESONANCE
ELECTRON TRANSFER
GENETIC ENGINEERING
IONS
MAGNETIC RESONANCE
MOLECULAR STRUCTURE
ORGANIC COMPOUNDS
PHOTOSYNTHETIC BACTERIA
PHOTOSYNTHETIC REACTION CENTERS
PROTEINS
RADICALS
REDOX REACTIONS
RESONANCE