Zang L H, Ghosh S, Maki A H
Department of Chemistry, University of California, Davis 95616.
Biochemistry. 1988 Oct 4;27(20):7820-5. doi: 10.1021/bi00420a035.
Triplet-state energies, zero-field splittings (ZFS), and total decay rate constants of the individual triplet-state sublevels of the tryptophan (Trp) residues located at positions 126, 138, and 158 in bacteriophage T4 lysozyme have been determined by using low-temperature phosphorescence and optical detection of magnetic resonance spectroscopy in zero applied magnetic field. An investigation of spectral and kinetic properties of individual Trp residues was facilitated by measurements on point-mutated proteins containing two Trp----Tyr substitutions. We find that the phosphorescence lifetime of the buried Trp-138 is considerably shorter than those of the solvent-exposed Trp residues. CH3HgII binding to cysteine residues in T4 lysozyme selectively perturbs the triplet state of Trp-158 by means of an external heavy-atom effect. In contrast with the previous observation of selective x-sublevel perturbation in the Trp-CH3Hg complex, the radiative character of the z sublevel (z is the out-of-plane axis) is selectively enhanced due to the heavy-atom perturbation of Trp-158. The observed pattern of radiative and total sublevel decay constants of the perturbed Trp is attributed to a special orientation of the Hg atom with respect to the indole plane.
通过在零外加磁场下使用低温磷光和磁共振光谱的光学检测，测定了噬菌体T4溶菌酶中位于126、138和158位的色氨酸（Trp）残基的三重态能量、零场分裂（ZFS）以及各个三重态子能级的总衰减速率常数。通过对含有两个Trp→Tyr取代的点突变蛋白进行测量，有助于对单个Trp残基的光谱和动力学性质进行研究。我们发现，埋藏的Trp-138的磷光寿命明显短于暴露于溶剂中的Trp残基的磷光寿命。T4溶菌酶中CH3HgII与半胱氨酸残基的结合通过外部重原子效应选择性地扰动Trp-158的三重态。与之前在Trp-CH3Hg配合物中观察到的选择性x子能级扰动相反，由于Trp-158的重原子扰动，z子能级（z是平面外轴）的辐射特性被选择性增强。观察到的受扰动Trp的辐射和总子能级衰减常数模式归因于Hg原子相对于吲哚平面的特殊取向。
