Site-directed mutagenesis identifies a tyrosine radical involved in the photosynthesized oxygen-evolving system
Photosynthetic oxygen evolution takes place in the thylakoid protein complex known as photosystem II. The reaction center core of this photosystem, where photochemistry occurs, is a heterodimer of homologous polypeptides called D1 and D2. Besides chlorophyll and quinone, photosystem II contains other organic cofactors, including two known as Z and D. Z transfers electrons from the site of water oxidation to the oxidized reaction center primary donor, P/sub 680//sup +/, while D /center dot//sup +/ gives rise to the dark-stable EPR spectrum known as signal II. D/center dot//sup +/ has recently been shown to be a tyrosine radical. Z is probably a second tyrosine located in a similar environment. Indirect evidence indicates that Z and D are associated with the D1 and E2 polypeptides, respectively. To identify the specific tyrosine residue corresponding to D, the authors have changed Tyr-160 of the D2 polypeptide to phenylalanine by site-directed mutagenesis of a psbD gene in the cyanobacterium Synechocystis 6803. The resulting mutant grows photosynthetically, but it lacks the EPR signal of D/center dot//sup +/. The authors conclude that D is Tyr-160 of the D2 polypeptide. They suggest that the C/sub 2/ symmetry in photosystem II extends beyond P/sub 680/ to its immediate electron donor and conclude that Z is Try-161 of the D1 polypeptide.
- Research Organization:
- Michigan State Univ., East Lansing, MI (United States)
- DOE Contract Number:
- AC02-76ER01338
- OSTI ID:
- 6143367
- Journal Information:
- Proc. Natl. Acad. Sci. U.S.A.; (United States), Vol. 85:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CYANOBACTERIA
ELECTRON SPIN RESONANCE
PHOTOSYNTHETIC REACTION CENTERS
BIOPHYSICS
DNA
DNA SEQUENCING
ELECTRON TRANSFER
MUTAGENESIS
PHOSPHORUS 32
PHOTOSYNTHESIS
TYROSINE
AMINO ACIDS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
DAYS LIVING RADIOISOTOPES
HYDROXY ACIDS
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
MICROORGANISMS
NUCLEI
NUCLEIC ACIDS
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
PHOSPHORUS ISOTOPES
PHOTOCHEMICAL REACTIONS
RADIOISOTOPES
RESONANCE
STRUCTURAL CHEMICAL ANALYSIS
SYNTHESIS
550201* - Biochemistry- Tracer Techniques