Primary donor triplet states of Photosystem I and II studied by Q-band pulse ENDOR spectroscopy

0568733 - BC 2023 RIV NL eng J - Journal Article
Niklas, J. - Agostini, Alessandro - Carbonera, D. - Di Valentin, M. - Lubitz, W.
Primary donor triplet states of Photosystem I and II studied by Q-band pulse ENDOR spectroscopy.
Photosynthesis Research. Roč. 152, č. 2 (2022), s. 213-234. ISSN 0166-8595. E-ISSN 1573-5079
R&D Projects: GA MŠMT(CZ) EF18_053/0016982
Institutional support: RVO:60077344
Keywords : Chlorophyll triplet state * Triplet EPR * endor * Spin density distribution * p680 * p700
OECD category: Biophysics
Impact factor: 3.7, year: 2022
Method of publishing: Open access
https://link.springer.com/article/10.1007/s11120-022-00905-y

The photoexcited triplet state of the 'primary donors' in the two photosystems of oxygenic photosynthesis has been investigated by means of electron-nuclear double resonance (ENDOR) at Q-band (34 GHz). The data obtained represent the first set of H-1 hyperfine coupling tensors of the (3)P700 triplet state in PSI and expand the existing data set for (3)P680. We achieved an extensive assignment of the observed electron-nuclear hyperfine coupling constants (hfcs) corresponding to the methine alpha-protons and the methyl group beta-protons of the chlorophyll (Chl) macrocycle. The data clearly confirm that in both photosystems the primary donor triplet is located on one specific monomeric Chl at cryogenic temperature. In comparison to previous transient ENDOR and pulse ENDOR experiments at standard X-band (9-10 GHz), the pulse Q-band ENDOR spectra demonstrate both improved signal-to-noise ratio and increased resolution. The observed ENDOR spectra for (3)P700 and (3)P680 differ in terms of the intensity loss of lines from specific methyl group protons, which is explained by hindered methyl group rotation produced by binding site effects. Contact analysis of the methyl groups in the PSI crystal structure in combination with the ENDOR analysis of (3)P700 suggests that the triplet is located on the Chl aMODIFIER LETTER PRIME (P-A) in PSI. The results also provide additional evidence for the localization of (3)P680 on the accessory Chl(D1) in PSII.
Permanent Link: https://hdl.handle.net/11104/0340043