title: Photosynthetic electron transport in genetically altered photosystem II reaction centers of chloroplasts.
abstract: Using a cotransformation system to identify chloroplast transformants in Chlamydomonas reinhardtii, we converted histidine-195 of the photosystem II reaction center D1 protein to a tyrosine residue. The mutants were characterized by a reduced quantum efficiency for photosynthetic oxygen evolution, which varied in a pH-dependent manner, a reduced capacity to oxidize artificial donors to photosystem II, and P680+ reduction kinetics (microsecond) that were essentially similar to wild type. In addition, a dark-stable radical was detected by ESR in mutant photosystem II particles but not in wild-type particles. This radical was similar in g value and lineshape to chlorophyll or carotenoid cations but could have arisen from a tyrosine-195 cation. The ability of the photosystem II trap (P680+) to oxidize tyrosine residues suggests that the mutant tyrosine residue could be used as a redox-sensitive probe to investigate the environment around the photosystem II trap.
authors.affiliation: Department of Plant Biology, Ohio State University, Columbus 43210.
authors.forename: R A
authors.initials: RA
authors.lastname: Roffey
authors.forename: J H
authors.initials: JH
authors.lastname: Golbeck
authors.forename: C R
authors.initials: CR
authors.lastname: Hille
authors.forename: R T
authors.initials: RT
authors.lastname: Sayre
mesh_terms: D000818:Animals; D002696:Chlamydomonas / Q000235:genetics* / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D016678:Genome; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes; D016297:Mutagenesis, Site-Directed; D010641:Phenotype; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics* / Q000378:metabolism; D045332:Photosystem II Protein Complex; D015183:Restriction Mapping
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D004247:DNA