Photosynthetic electron transport in genetically altered photosystem II reaction centers of chloroplasts.
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.
Roffey
R A
RA
Department of Plant Biology, Ohio State University, Columbus 43210.
Golbeck
J H
JH
Hille
C R
CR
Sayre
R T
RT
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
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D004247:DNA