Characterization of carotenoid and chlorophyll photooxidation in photosystem II

C. A. Tracewell, A. Cua, D. H. Stewart, D. F. Bocian, Gary W Brudvig

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Abstract

Photosystem II (PSII) contains two accessory chlorophylls (ChlZ, ligated to D1-His118, and ChlD, ligated to D2-His117), carotenoid (Car), and heme (cytochrome b559) cofactors that function as alternate electron donors under conditions in which the primary electron-donation pathway from the O2-evolving complex to P680+ is inhibited. The photooxidation of the redox-active accessory chlorophylls and Car has been characterized by near-infrared (near-IR) absorbance, shifted-excitation Raman difference spectroscopy (SERDS), and electron paramagnetic resonance (EPR) spectroscopy over a range of cryogenic temperatures from 6 to 120 K in both Synechocystis PSII core complexes and spinach PSII membranes. The following key observations were made: (1) only one Chl+ near-IR band is observed at 814 nm in Synechocystis PSII core complexes, which is assigned to ChlZ + based on previous spectroscopic studies of the D1-H118Q and D2-H117Q mutants [Stewart, D. H., Cua, A., Chisholm, D. A., Diner, B. A., Bocian, D. F., and Brudvig, G. W. (1998) Biochemistry 37, 10040-10046]; (2) two Chl+ near-IR bands are observed at 817 and 850 nm in spinach PSII membranes which are formed with variable relative yields depending on the illumination temperature and are assigned to ChlZ +, and ChlD +, respectively; (3) the Chl and Car cation radicals have significantly different stabilities at reduced temperatures with Car+ decaying much faster; (4) in Synechocystis PSII core complexes, Car+ decays by recombination with QA - and not by ChlZ/ChlD oxidation, with multiphasic kinetics that are attributed to an ensemble of protein conformers that are trapped as the protein is frozen; and (5) in spinach PSII membranes, Car+ decays mainly by recombination with QA -, but also partly by formation of the 850 nm Chl cation radical. The greater stability of ChlZ + at low temperatures enabled us to confirm that resonance Raman bands previously assigned to ChlZ + are correctly assigned. In addition, the formation and decay of these cations provide insight into the alternate electron-donation pathways to P680+.

Original languageEnglish
Pages (from-to)193-203
Number of pages11
JournalBiochemistry
Volume40
Issue number1
DOIs
Publication statusPublished - Jan 9 2001

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Photosystem II Protein Complex
Photooxidation
Carotenoids
Chlorophyll
Synechocystis
Spinacia oleracea
Cations
Temperature
Accessories
Electrons
Infrared radiation
Membranes
Genetic Recombination
Spectroscopy
Biochemistry
Raman Spectrum Analysis
Electron Spin Resonance Spectroscopy
Lighting
Heme
Cryogenics

ASJC Scopus subject areas

  • Biochemistry

Cite this

Characterization of carotenoid and chlorophyll photooxidation in photosystem II. / Tracewell, C. A.; Cua, A.; Stewart, D. H.; Bocian, D. F.; Brudvig, Gary W.

In: Biochemistry, Vol. 40, No. 1, 09.01.2001, p. 193-203.

Research output: Contribution to journalArticle

Tracewell, C. A. ; Cua, A. ; Stewart, D. H. ; Bocian, D. F. ; Brudvig, Gary W. / Characterization of carotenoid and chlorophyll photooxidation in photosystem II. In: Biochemistry. 2001 ; Vol. 40, No. 1. pp. 193-203.
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AU - Brudvig, Gary W

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