APPLICATION OF 140 GHZ PULSED ENDOR TO CLASS I RNRS

高场ENDOR的一个主要应用是在表演 EPR谱线不同场位的超精细测量 与高选择性分子的激发相对应 方向。由于g-各向异性色散随 外加磁场，140 GHz的Endor谱揭示场 依赖的粉末图案提供了大量的约束 用于超细管接头的测定。我们用了这个 研究分子的电子和化学结构的技术 酪氨酸基存在于不同的I类RNRs中，例如来自E. 大肠杆菌和酵母菌。得到了随磁场变化的Endor谱 具有高信噪比(&gt；20)，并展示了基本的新功能 在X波段实验中无法辨别。编制了一个模拟程序 开发的目的是提取超精细张量和结构 反映在超细粒子相对取向上的信息 电子塞曼g张量的张量。从分析 大肠杆菌酪氨酸基的实验光谱和模拟光谱 得到了弱耦合的超精细耦合的一种新的赋值 耦合的2，6环和~亚甲基质子。Endor谱的比较 证实在质子化和置换水基质中存在RNR酶 弱耦合氢键质子的缺失。相反，恩多 酵母菌的光谱揭示了一些新的特征，我们将其归类为 氢键的存在。酵母的Endor实验 酪氨酸基目前正在进行中。

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.