APPLICATION OF 140 GHZ PULSED ENDOR TO CLASS I RNRS

高场ENDOR的一个主要应用在于执行 EPR谱线上不同场位置的超精细测量 对应于高度选择的分子的激发 方向。 由于g-各向异性色散与 外部磁场，140 GHz ENDOR光谱显示场 提供大量约束的依赖粉末图案 用于超精细耦合的测定。 我们用这个 技术来研究电子和化学结构的 酪氨酰自由基在不同的I类RNR中，如来自细菌E. 大肠杆菌和酵母菌。 获得了磁场依赖的ENDOR谱 具有高信噪比（> 20），并揭示了重要的新特征 在X波段实验中没有发现。 一个模拟程序， 为了提取超精细张量和结构 信息反映在相对取向的超精细 电子塞曼g张量。 从分析 E.大肠杆菌酪氨酰自由基，我们 得到了一个新的指定的超精细耦合的弱 偶联的2，6-环和~亚甲基质子。 ENDOR光谱的比较 质子化和全氘化水基质中的RNR酶证实 缺少弱耦合的氢键质子。 相反，ENDOR 酵母的光谱揭示了一些新的功能，我们分配给 氢键的存在。 酵母的ENDOR实验 酪氨酰自由基目前正在进行中。

A major application of high field ENDOR consists in performing hyperfine measurements at different field positions in the EPR line corresponding to the excitation of highly selected molecular orientations. Since the g-anisotropy dispersion scales with the external magnetic field, the 140 GHz ENDOR spectra reveal field dependent powder patterns that provide a large number of constraints for the determination of the hyperfine couplings. We used this technique to investigate the electronic and chemical structure of the tyrosyl radical in different Class I RNRs, such as from bacterium E. coli and Yeast. Magnetic field dependent ENDOR spectra were obtained with high signal-to-noise (> 20) and revealed essential new features not discerned in X-band experiments. A simulation program was developed in order to extract hyperfine tensors and structural informations reflected in the relative orientation of the hyperfine tensor to the electronZeeman g-tensor. From the analysis of the experimental and simulated spectra of the E. coli tyrosyl radical, we obtained a new assignment for the hyperfine couplings of the weakly coupled 2,6-ring and ~methylene protons. Comparison of ENDOR spectra of a RNR enzyme in protonated and perdeutated water matrix confirmed the absence of weakly coupled hydrogen-bonded protons. Instead, ENDOR spectra of the Yeast revealed some new features, which we assign to the presence of hydrogen bonds. ENDOR experiments on the Yeast tyrosyl radical are currently in progress.