Tsao D H, Maki A H, Chase J W
Department of Chemistry, University of California, Davis 95616.
FEBS Lett. 1990 Feb 26;261(2):389-91. doi: 10.1016/0014-5793(90)80599-e.
The complexes of point-mutated Escherichia coli single-stranded DNA-binding protein (Eco SSB) with poly-(2-thiouridylic acid) (poly S2U) have been studied by optical detection of magnetic resonance spectroscopy (ODMR). Previous work has determined that two of four tryptophan (Trp) residues in Eco SSB undergo stacking interactions with nucleic acid bases. Selective photoexcitation of S2U bases was performed and subsequent triplet----triplet energy transfer from S2U to nearby Trp residues in the protein took place. The zero-field splitting (ZFS) parameters and sublevel kinetics were determined for each Trp residue sensitized by S2U. The sublevel lifetimes of the two sensitized residues are similar to those of normal Trp. The ZFS parameters, on the other hand, show a dramatic reduction relative to those of the uncomplexed protein, implying a more polarizable environment for the sensitized Trp residues and/or charge transfer interactions with the S2U bases.
通过磁共振光谱的光学检测（ODMR）研究了点突变的大肠杆菌单链DNA结合蛋白（Eco SSB）与聚（2-硫代尿苷酸）（聚S2U）的复合物。先前的工作已经确定，Eco SSB中四个色氨酸（Trp）残基中的两个与核酸碱基发生堆积相互作用。对S2U碱基进行了选择性光激发，随后发生了从S2U到蛋白质中附近Trp残基的三重态-三重态能量转移。确定了由S2U敏化的每个Trp残基的零场分裂（ZFS）参数和子能级动力学。两个敏化残基的子能级寿命与正常Trp的相似。另一方面，ZFS参数相对于未复合蛋白的参数显示出显著降低，这意味着敏化的Trp残基具有更可极化的环境和/或与S2U碱基的电荷转移相互作用。
