Nitroxide Side-Chain Dynamics in a Spin-Labeled Helix-Forming Peptide Revealed by High-Frequency (139.5-GHz) EPR Spectroscopy
✍ Scribed by M. Bennati; G.J. Gerfen; G.V. Martinez; R.G. Griffin; D.J. Singel; G.L. Millhauser
- Book ID
- 102599243
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 106 KB
- Volume
- 139
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
High-frequency electron paramagnetic resonance (EPR) spectroscopy has been performed on a nitroxide spin-labeled peptide in fluid aqueous solution. The peptide, which follows the single letter sequence, was reacted with the methanethiosulfonate spin label at the cysteine sulfur. The spin sensitivity of high-frequency EPR is excellent with less than 20 pmol of sample required to obtain spectra with good signal-to-noise ratios. Simulation of the temperature-dependent spectral lineshapes reveals the existence of local anisotropic motion about the nitroxide N-O bond with a motional anisotropy tau( perpendicular)/tau( parallel) ( identical with N) approaching 2.6 at 306 K. Comparison with previous work on rigidly labeled peptides suggests that the spin label is reorienting about its side-chain tether. This study demonstrates the feasibility of performing 140-GHz EPR on biological samples in fluid aqueous solution.