Absolute signs of hyperfine coupling constants as determined by pulse ENDOR of polarized radical pairs

Epel, Boris; Niklas, Jens; Antonkine, Mikhail L.; Lubitz, Wolfgang

doi:10.1007/bf03166203

Cited by 12 publications

(22 citation statements)

References 46 publications

(62 reference statements)

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“…To clarify whether they arise from one or two 13 C HFI tensors, we also performed variable mixing time (VMT) Mims-ENDOR experiments which measure the absolute signs of the HFI tensors. 46 The VMT Mims-ENDOR collected at g =1.936 (Figure S3), g 2 of H hyd , indicates that the two sets of peaks do not change in the same manner as t mix is increased from 1 μs to 200 μs, and they also have oppositely signed HFI. Therefore, they must correspond to two different HFI tensors.…”

Section: Resultsmentioning

confidence: 98%

Electronic Structure of Two Catalytic States of the [FeFe] Hydrogenase H-Cluster As Probed by Pulse Electron Paramagnetic Resonance Spectroscopy

Rao

Britt

2018

Inorg. Chem.

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The active site of the [FeFe] hydrogenase (HydA1), the H-cluster, is a 6-Fe cofactor that contains CO and CN ligands. It undergoes several different oxidation and protonation state changes in its catalytic cycle to metabolize H. Among them, the well-known H state and the recently identified H state are thought to be directly involved in H activation and evolution, and they are both EPR active with net spin S = 1/2. Herein, we report the pulse electronic paramagnetic spectroscopic investigation of these two catalytic states in Chlamydomonas reinhardtii HydA1 ( CrHydA1). Using an in vitro biosynthetic maturation approach, we site-specifically installed C into the CO or CN ligands and Fe into the [2Fe] subcluster of the H-cluster in order to measure the hyperfine couplings to these magnetic nuclei. For H, we measured C hyperfine couplings (CO a of 25.5, 5.8, and 4.5 MHz) corresponding to all three CO ligands in the H-cluster. We also observed two Fe hyperfine couplings (Fe a of ∼17 and 5.7 MHz) arising from the two Fe atoms in the [2Fe] subcluster. For H, we only observed two distinct CO hyperfine interactions (CO a of 0.16 and 0.08 MHz) and only one for CN (CN a of 0.16 MHz); the couplings to the CO/CN on the distal Fe of [2Fe] may be too small to detect. We also observed a very small (<0.3 MHz) Fe HFI from the labeled [2Fe] subcluster and four Fe HFI from the labeled [4Fe-4S] subcluster (Fe a of 7.2, 16.6, 28.2, and 35.3 MHz). These hyperfine coupling constants are consistent with the previously proposed electronic structure of the H-cluster at both H and H states and provide a basis for more detailed analysis.

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Section: Resultsmentioning

confidence: 98%

Electronic Structure of Two Catalytic States of the [FeFe] Hydrogenase H-Cluster As Probed by Pulse Electron Paramagnetic Resonance Spectroscopy

Rao

Britt

2018

Inorg. Chem.

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“…This was utilized in pulse ENDOR studies of the laser flash generated spin-polarized RP (Fursmann et al 2002 ; Epel et al 2006 ). The Q-band transient EPR spectrum of this RP is shown in the top panel of Fig.…”

Section: Examples Of Applicationmentioning

confidence: 99%

“…B : Comparison of 1 H ENDOR spectra of the stationary radical (photo chemical reduction of PSI) and the short-lived RP state obtained near g x ( ) where the contribution is very small. For details see Niklas et al ( 2009 ), Epel et al ( 2006 ) …”

Section: Examples Of Applicationmentioning

confidence: 99%

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Electron-nuclear double resonance

Кулик

Lubitz²

2009

Photosynth Res

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The application of electron-nuclear double resonance (ENDOR) spectroscopy for the investigation of photosynthetic systems is reviewed. The basic principles of continuous wave and pulse ENDOR are presented. Selected examples of the application of the ENDOR technique for studying stable and transient paramagnetic species, including cofactor radical ions, radical pairs, triplet states, and the oxygen-evolving complex in plant Photosystem II (PSII) are discussed. Limitations and perspectives of ENDOR spectroscopy are outlined.

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“…The contribution of P 700 ·+ to the ENDOR spectra at this position is still rather small [48]. At this spectral position, both emissive and absorptive EPR transitions are excited.…”

Section: Resultsmentioning

confidence: 99%

Investigation of the Stationary and Transient A 1 ·− Radical in Trp → Phe Mutants of Photosystem I

Niklas¹,

Gopta

Epel³

et al. 2009

Appl Magn Reson

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Photosystem I (PS I) contains two symmetric branches of electron transfer cofactors. In both the A- and B-branches, the phylloquinone in the A1 site is π-stacked with a tryptophan residue and is H-bonded to the backbone nitrogen of a leucine residue. In this work, we use optical and electron paramagnetic resonance (EPR) spectroscopies to investigate cyanobacterial PS I complexes, where these tryptophan residues are changed to phenylalanine. The time-resolved optical data show that backward electron transfer from the terminal electron acceptors to P700·+ is affected in the A- and B-branch mutants, both at ambient and cryogenic temperatures. These results suggest that the quinones in both branches take part in electron transport at all temperatures. The electron-nuclear double resonance (ENDOR) spectra of the spin-correlated radical pair P700·+A1·− and the photoaccumulated radical anion A1·−, recorded at cryogenic temperature, allowed the identification of characteristic resonances belonging to protons of the methyl group, some of the ring protons and the proton hydrogen-bonded to phylloquinone in the wild type and both mutants. Significant changes in PS I isolated from the A-branch mutant are detected, while PS I isolated from the B-branch mutant shows the spectral characteristics of wild-type PS I. A possible short-lived B-branch radical pair cannot be detected by EPR due to the available time resolution; therefore, only the A-branch quinone is observed under conditions typically employed for EPR and ENDOR spectroscopies.

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Absolute signs of hyperfine coupling constants as determined by pulse ENDOR of polarized radical pairs

Cited by 12 publications

References 46 publications

Electronic Structure of Two Catalytic States of the [FeFe] Hydrogenase H-Cluster As Probed by Pulse Electron Paramagnetic Resonance Spectroscopy

Electronic Structure of Two Catalytic States of the [FeFe] Hydrogenase H-Cluster As Probed by Pulse Electron Paramagnetic Resonance Spectroscopy

Electron-nuclear double resonance

Investigation of the Stationary and Transient A 1 ·− Radical in Trp → Phe Mutants of Photosystem I

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