Lin Myat T, Samoilova Rimma I, Gennis Robert B, Dikanov Sergei A
Department of Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
J Am Chem Soc. 2008 Nov 26;130(47):15768-9. doi: 10.1021/ja805906a.
The selective (15)N isotope labeling was used for the identification of the nitrogen involved in a hydrogen bond formation with the semiquinone in the high-affinity Q(H) site in the cytochrome bo(3) ubiquinol oxidase. This nitrogen produces dominating contribution to X-Band (14)N ESEEM spectra. The 2D ESEEM (HYSCORE) experiments with the Q(H) site SQ in the series of selectively (15)N labeled bo(3) oxidase proteins have directly identified the N(epsilon) of R71 as an H-bond donor. In addition, selective (15)N labeling has allowed us for the first time to determine weak hyperfine couplings with the side-chain nitrogens from all residues around the SQ. Those are reflecting a distribution of the unpaired spin density over the protein in the SQ state of the quinone processing site.
采用选择性（15）N同位素标记来鉴定与细胞色素bo（3）泛醇氧化酶高亲和力Q（H）位点中的半醌形成氢键的氮。该氮对X波段（14）N电子自旋回波包络调制（ESEEM）光谱有主要贡献。在一系列选择性（15）N标记的bo（3）氧化酶蛋白中，对Q（H）位点半醌进行二维ESEEM（高分辨二维电子自旋回波包络调制，HYSCORE）实验，直接确定R71的N（ε）作为氢键供体。此外，选择性（15）N标记首次使我们能够确定与半醌周围所有残基的侧链氮的弱超精细耦合。这些反映了醌处理位点处于半醌状态时蛋白质上未配对自旋密度的分布。
