Journal
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
Volume 363, Issue 1494, Pages 1157-1166Publisher
ROYAL SOC
DOI: 10.1098/rstb.2007.2211
Keywords
multifrequency electron spin-echo envelope modulation; histidine ligation; manganese cluster; photosystem II
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Funding
- NIGMS NIH HHS [GM 66136, R29 GM048242, GM 48242, R01 GM066136, R01 GM048242] Funding Source: Medline
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The CalEPR Center at UC-Davis (http:// brittepr.ucdavis.edu) is equipped with five research grade electron paramagnetic resonance (EPR) instruments operating at various excitation frequencies between 8 and 130 GHz. Of particular note for this RSC meeting are two pulsed EPR spectrometers working at the intermediate microwave frequencies of 31 and 35 GHz. Previous lower frequency electron spin-echo envelope modulation (ESEEM) studies indicated that histidine nitrogen is electronically coupled to the Mn cluster in the S-2 state of photosystem II (PSII). However, the amplitude and resolution of the spectra were relatively poor at these low frequencies, precluding any in-depth analysis of the electronic structure properties of this closely associated nitrogen nucleus. With the intermediate frequency instruments, we are much closer to the 'exact cancellation' limit, which optimizes ESEEM spectra for hyperfine-coupled nuclei such as N-14 and N-15. Herein, we report the results from ESEEM studies of both N-14- and N-15-labelled PSII at these two frequencies. Spectral simulations were constrained by both isotope datasets at both frequencies, with a focus on high-resolution spectral examination of the histidine ligation to the Mn cluster in the S-2 state.
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