NITROXIDE SIDE CHAIN DYNAMICS IN SPIN LABELED HELIX FORMING PEPTIDE

进行了高频电子顺磁共振 在流体水溶液中的氮氧自旋标记肽上。 的 肽，其遵循单字母序列 Ac-（AAAAK）2CAAAKA-NH 2与甲硫基磺酸盐自旋反应， 标记在半胱氨酸硫上。 高频自旋灵敏度 EPR非常出色，所需样品不到50纳克， 获得具有良好信噪比的光谱。 模拟 温度依赖的光谱线型揭示了 氮氧自由基N-0键的局域各向异性运动， 各向异性，rl/，rll（=- N）在306 K时接近2.6。相比 先前对刚性标记肽的研究表明， 是围绕着它的侧链重新定向。 本研究证明 在生物样品上进行140 GHz EPR的可行性， 流体溶液

High frequency electron paramagnetic resonance has been performed on a nitroxide spin labeled peptide in fluid aqueous solution. The peptide, which follows the single letter sequence Ac-(AAAAK)2CAAAKA-NH2 was reacted with the methanethiosulfonate spin label at the cystein sulfur. The spin sensitivity of high frequency EPR is excellent with less than fifty nanograms 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-0 bond with a motional anisotropy ,rl/,rll (=- 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. The study demonstrated the feasibility of performing 140 GHz EPR on biological samples in fluid solution.