Abstract
The underlying causes of asymmetric intensities in Davies pulsed ENDOR spectra that are associated with the signs of the hyperfine interaction are reinvestigated. The intensity variations in these asymmetric ENDOR patterns are best described as shifts in an apparent baseline intensity that occurs dynamically following on-resonance ENDOR transitions. We have developed an extremely straightforward multi-sequence protocol that is capable of giving the sign of the hyperfine interaction by probing a single ENDOR transition, without reference to its partner transition. This technique, Pulsed ENDOR Saturation and Recovery (PESTRE) monitors dynamic shifts in the 'baseline' following measurements at a single RF frequency (single ENDOR peak), rather than observing anomalous ENDOR intensity differences between the two branches of an ENDOR response. These baseline shifts, referred to as dynamic reference levels (DRLs), can be directly tied to the electron-spin manifold from which that ENDOR transition arises. The application of this protocol is demonstrated on 57Fe ENDOR of a 2Fe-2S ferredoxin. We use the 14N ENDOR transitions of the S = 3/2[Fe(II)NO]2+ center of the non-heme iron enzyme, anthranilate dioxygenase (AntDO) to examine the details of the relaxation model using PESTRE.
Original language | English (US) |
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Pages (from-to) | 76-86 |
Number of pages | 11 |
Journal | Journal of Magnetic Resonance |
Volume | 208 |
Issue number | 1 |
DOIs | |
State | Published - Jan 2011 |
Funding
The author is grateful for extensive and helpful discussions with Prof. Brian M. Hoffman, Northwestern University, the input of Prof. Joshua Telser, Roosevelt University as well as Mr. Adam Kinney, Northwestern University. The work could not have been completed without the technical wizardry of Mr. Clark Davoust, who built and maintains the spectrometer. We thank Prof. Donald Kurtz for the AntDO enzyme sample. We also thank Prof. Jacques Meyer (Grenoble) for the ferredoxin sample. This work was supported by the NIH (HL-13531).
Keywords
- ENDOR
- EPR
- Hyperfine tensor
- Nuclear relaxation
ASJC Scopus subject areas
- Condensed Matter Physics
- Nuclear and High Energy Physics
- Biophysics
- Biochemistry