Tyrosine radicals in photosystem II and related model compounds. Characterization by isotopic labeling and EPR spectroscopy

Journal Article · Sun Nov 25 04:00:00 EST 1990 · Journal of Biological Chemistry; (USA)

OSTI ID:6324135

Barry, B A; El-Deeb, M K; Sandusky, P O; Babcock, G T ^[1]

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1. Michigan State Univ., East Lansing (USA)

Deuteration at selected positions on the phenol ring and at the beta-methylene carbon for the YD.tyrosine radical in Photosystem II in the cyanobacterium Synechocystis 6803 was achieved by growing the organism under conditions in which it is a functional aromatic amino acid auxotroph. A series of model tyrosine radicals, also deuterated at specific sites on the aromatic ring and the methylene group, was generated by UV irradiation of frozen solutions. The EPR spectra of the specifically deuterated in vivo radicals confirm that YD.is a tyrosine; nevertheless its spectra differ from those of the tyrosine models. By comparing the EPR spectra of the specifically deuterated radicals with those of the fully protonated, the hyperfine couplings of the various protons of both YD.and the model compound radicals were determined. For both species, the unpaired electron spin density distribution is essentially identical and follows an odd-alternant pattern with high rho values at the carbons ortho and para to the tyrosine phenol oxygen; the meta positions have low spin densities. The differences in EPR spectral characteristics for the two radicals are rationalized as arising from variations in the conformation of the beta-methylene group with respect to the phenol head group. Considering these EPR results and those reported for other model and naturally occurring tyrosine radicals, we conclude that this situation is general; there is little deviation in this class of compounds from the odd-alternant spin density distribution; variations in EPR lineshapes arise primarily from variations in beta-methylene orientation. The conformation of the -CH2- group in biologically active tyrosine radicals deviates from that observed in the models and may be functionally significant.

• OSTI ID: 6324135
• Journal Information: Journal of Biological Chemistry; (USA), Journal Name: Journal of Biological Chemistry; (USA) Vol. 265:33; ISSN JBCHA; ISSN 0021-9258
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
560130 -- Radiation Effects on Microorganisms
59 BASIC BIOLOGICAL SCIENCES
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
AMINO ACIDS
CARBOXYLIC ACIDS
CYANOBACTERIA
DEUTERIUM
ELECTROMAGNETIC RADIATION
ELECTRON SPIN RESONANCE
HYDROGEN ISOTOPES
HYDROXY ACIDS
ISOTOPE APPLICATIONS
ISOTOPE DILUTION
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
MATHEMATICAL MODELS
MICROORGANISMS
MOLECULAR STRUCTURE
NUCLEI
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
PHOTOSYNTHETIC REACTION CENTERS
RADIATIONS
RADICALS
RESONANCE
STABLE ISOTOPES
TRACER TECHNIQUES
TYROSINE
ULTRAVIOLET RADIATION