EPR characterization of genetically modified reaction centers of Rhodobacter capsulatus
| Autor: | Edward J. Bylina, Douglas C. Youvan, James R. Norris, Stephen V. Kolaczkowski |
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| Rok vydání: | 1990 |
| Předmět: |
Photosynthetic reaction centre
Photosynthetic Reaction Center Complex Proteins Light-Harvesting Protein Complexes macromolecular substances Zero field splitting Photochemistry Biochemistry law.invention Electron Transport Electron transfer law Pyrroles Triplet state Electron paramagnetic resonance Bacteriochlorophylls Rhodobacter biology Tetrapyrrole binding Chemistry Electron Spin Resonance Spectroscopy Pheophytins biology.organism_classification Rhodospirillaceae Crystallography Unpaired electron Tetrapyrroles Mutation Oxidation-Reduction |
| Zdroj: | Biochemistry. 29(26) |
| ISSN: | 0006-2960 |
| Popis: | 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 inmore » 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.« less |
| Databáze: | OpenAIRE |
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