High-field EPR study of carotenoid and chlorophyll cation radicals in photosystem II.
In photosystem II (PS II), chlorophyll, {beta}-carotene, and cytochrome b{sub 559} are alternate electron donors that may be involved in a photoprotection mechanism. The present study describes the use of high-field EPR spectroscopy to characterize the low-temperature photooxidation of Chl{sub z} and Car cofactors in PS II. The EPR signals of the individual species, previously not resolved at X-band frequency (9 GHz), are resolved at higher D-band frequency (130 GHz) in deuterated Synechococcus lividus PS II. Deuteration of PS II results in significant narrowing of the EPR lines, yielding well-resolved EPR spectra of the Car{sup +} and Chl{sub z}{sup +} radicals at 130 GHz. The g tensors of the individual species were determined by EPR spectral simulations. The g tensor determined for the Car{sup +} radical (g{sub xx} = 2.00335, g{sub yy} = 2.00251, g{sub zz} = 2.00227) is similar to that previously observed for a canthaxanthin cation radical but with a slightly rhombic tensor. The Chl{sub z}{sup +} g tensor (g{sub xx} = 2.00312, g{sub yy} = 2.00263, g{sub zz} = 2.00202) is similar to that of a chlorophyll a cation radical. This study shows that both the carotenoid and chlorophyll radicals are generated in PS II by illumination at temperatures from 6 to 190 K and that there is no interconversion of Car{sup +} and Chl{sub z}{sup +} radicals upon dark annealing at temperatures up to 160 K. This study also establishes the feasibility of using deuteration and high-field EPR to resolve previously unresolvable cofactor signals in PS II.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); National Institutes of Health (NIH)
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 943111
- Report Number(s):
- ANL/CHM/JA-37543; JPCBFK; TRN: US201002%%600
- Journal Information:
- J. Phys. Chem. B, Vol. 104, Issue 45 ; Nov. 16, 2000; ISSN 1089-5647
- Country of Publication:
- United States
- Language:
- ENGLISH
Similar Records
Structure of the P{sup +{sub 700}}A{sup -{sub 1}} radical pair intermediate in photosystem I by high time resolution multifrequency electron paramagnetic resonance - analysis of quantum beat oscillations.
Magnetic field induced orientation of photosynthetic reaction centers as revealed by time-resolved D-band electron paramagnetic resonance of spin-correlated radical pairs. II. Field dependence of the alignment.
Related Subjects
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
ANNEALING
BINDING ENERGY
CAROTENOIDS
CATIONS
CHLOROPHYLL
CYTOCHROMES
DEUTERATION
ELECTRON SPIN RESONANCE
ELECTRONS
ILLUMINANCE
RADICALS
SIGNALS
SPECTRA
SPECTROSCOPY
TEMPERATURE RANGE 0065-0273 K
TENSORS
VALENCE