Chlorophyll and Carotenoid Radicals in Photosystem II Studied by Pulsed ENDOR
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- 作者：Peter Faller ; Thorsten Maly ; A. William Rutherford ; and Fraser MacMillan
- 刊名：Biochemistry
- 出版年：2001
- 出版时间：January 16, 2001
- 年：2001
- 卷：40
- 期：2
- 页码：320 - 326
- 全文大小：78K
- 年卷期：v.40,no.2(January 16, 2001)
- ISSN：1520-4995
文摘
The stable carotenoid cation radical (Car
+) and chlorophyll cation radical (ChlZ+) inphotosystem 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 wereattributed to Car+ and ChlZ+ on the basis of their characteristic behavior with temperature as demonstratedearlier [Hanley et al. (1999) Biochemistry 38, 8189-8195]: i.e., (a) the Car+ alone was generated byillumination at 
20 K, while ChlZ+ alone was generated at 200 K, and (b) warming of the samplecontaining the Car+ to 200 K resulted in the loss of the signal attributable to Car+ and its replacementby a spectrum attributable to the ChlZ+. A map of the hyperfine structure of Car+ in PS II and in organicsolvent was obtained. The largest observed hyperfine splitting for Car+ in either environment was in theorder of 8-9 MHz. Thus, the spin density on the cation is proposed to be delocalized over the carotenoidmolecule. The pulsed ENDOR spectrum of ChlZ+ was compared to that obtained from a Chl a cation infrozen organic solvent. The hyperfine coupling constants attributed to the 
-protons at position 17 and 18are well resolved from ChlZ+ in PS II (10.8 and 14.9 MHz) but not in Chl a+ in organic solvent (12.5MHz). This suggests a more defined conformation of ring IV with respect to the rest of the tetrapyrrolering plane of ChlZ+ than Chl a+ probably induced by the protein matrix.
+) and chlorophyll cation radical (ChlZ+) inphotosystem 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 wereattributed to Car+ and ChlZ+ on the basis of their characteristic behavior with temperature as demonstratedearlier [Hanley et al. (1999) Biochemistry 38, 8189-8195]: i.e., (a) the Car+ alone was generated byillumination at 20 K, while ChlZ+ alone was generated at 200 K, and (b) warming of the samplecontaining the Car+ to 200 K resulted in the loss of the signal attributable to Car+ and its replacementby a spectrum attributable to the ChlZ+. A map of the hyperfine structure of Car+ in PS II and in organicsolvent was obtained. The largest observed hyperfine splitting for Car+ in either environment was in theorder of 8-9 MHz. Thus, the spin density on the cation is proposed to be delocalized over the carotenoidmolecule. The pulsed ENDOR spectrum of ChlZ+ was compared to that obtained from a Chl a cation infrozen organic solvent. The hyperfine coupling constants attributed to the -protons at position 17 and 18are well resolved from ChlZ+ in PS II (10.8 and 14.9 MHz) but not in Chl a+ in organic solvent (12.5MHz). This suggests a more defined conformation of ring IV with respect to the rest of the tetrapyrrolering plane of ChlZ+ than Chl a+ probably induced by the protein matrix.