Chlorophyll and carotenoid radicals in photosystem II studied by pulsed ENDOR.
The stable carotenoid cation radical (Car(*+)) and chlorophyll cation radical (Chl(Z)(*+)) in photosystem II (PS II) have been studied by pulsed electron nuclear double resonance (ENDOR) spectroscopy. The spectra were essentially the same for oxygen-evolving PS II and Mn-depleted PS II. The radicals were generated by illumination given at low temperatures, and the ENDOR spectra were attributed to Car(*)(+) and Chl(Z)(*+) on the basis of their characteristic behavior with temperature as demonstrated earlier [Hanley et al. (1999) Biochemistry 38, 8189-8195]: i.e., (a) the Car(*)(+) alone was generated by illumination at < or =20 K, while Chl(Z)(*+) alone was generated at 200 K, and (b) warming of the sample containing the Car(*+) to 200 K resulted in the loss of the signal attributable to Car(*+) and its replacement by a spectrum attributable to the Chl(Z)(*+). A map of the hyperfine structure of Car(*+) in PS II and in organic solvent was obtained. The largest observed hyperfine splitting for Car(*+) in either environment was in the order of 8-9 MHz. Thus, the spin density on the cation is proposed to be delocalized over the carotenoid molecule. The pulsed ENDOR spectrum of Chl(Z)(*)(+) was compared to that obtained from a Chl a cation in frozen organic solvent. The hyperfine coupling constants attributed to the beta-protons at position 17 and 18 are well resolved from Chl(Z)(*+) in PS II (10. 8 and 14.9 MHz) but not in Chl a(*+) in organic solvent (12.5 MHz). This suggests a more defined conformation of ring IV with respect to the rest of the tetrapyrrole ring plane of Chl(Z)(*+) than Chl a(*+) probably induced by the protein matrix.
Faller
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Institut für Physikalische und Theoretische Chemie, Johann Wolfgang Département de Biologie Cellulaire et Moléculaire, CNRS URA 2096, CEA Saclay, F-91191, France.
Maly
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Rutherford
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MacMillan
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D002338:Carotenoids / Q000737:chemistry*; D002412:Cations; D002734:Chlorophyll / Q000737:chemistry*; D000077194:Chlorophyll A; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004579:Electron Transport; D005609:Free Radicals / Q000737:chemistry; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism; D045342:Light-Harvesting Protein Complexes; D008345:Manganese / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D018724:Spinacia oleracea
D002412:Cations; D005609:Free Radicals; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D002338:Carotenoids; D008345:Manganese; D000077194:Chlorophyll A