Chlorophyll and carotenoid radicals in photosystem II studied by pulsed ENDOR

Faller, Peter, Maly, Thorsten, Rutherford, A. William and Macmillan, Fraser ORCID: https://orcid.org/0000-0002-2410-4790 (2001) Chlorophyll and carotenoid radicals in photosystem II studied by pulsed ENDOR. Biochemistry, 40 (2). pp. 320-326. ISSN 0006-2960

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Abstract

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 less than or equal to 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.

Item Type: Article
Faculty \ School: Faculty of Science > School of Chemistry
Depositing User: Rachel Smith
Date Deposited: 19 Jul 2011 11:09
Last Modified: 24 Oct 2022 03:37
URI: https://ueaeprints.uea.ac.uk/id/eprint/33885
DOI: 10.1021/bi002029l

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