Cha T A, Maki A H
J Biol Chem. 1984 Jan 25;259(2):1105-9.
Optically detected triplet state magnetic resonance spectra are reported for the complex formed between mercurated poly(Urd) and Escherichia coli single-stranded DNA binding protein. Upon forming a complex, the triplet state properties of Trp residue(s) in the protein are perturbed by the heavy mercury atom and are characterized by a shortened triplet state lifetime and the appearance of a strong D + E slow passage optically detected magnetic resonance signal. These features, which signal an external heavy atom effect, provide direct evidence for a close range interaction between mercurated nucleotide bases and Trp residues owing to the requirement of a van der Waals contact between the perturbed molecule and the heavy atom perturber. The amplitude-modulated phosphorescence microwave double resonance technique selectively displays the phosphorescence spectrum of the heavy atom-perturbed Trp triplet states. A van der Waals contact manifested through a stacked structure of the mercurated uridine base and the indole moiety of Trp is strongly suggested as the most plausible mode of interaction from steric considerations, since other approaches of the mercury atom are blocked by the covalent attachment of 2-mercaptoethanol to mercury. The magnitude of the heavy atom perturbation also is consistent with Hg approach to the pi-system from above or below the indole aromatic plane, and is at least an order of magnitude larger than effects expected from an edge-on approach.
报道了汞化聚尿苷酸（mercurated poly(Urd)）与大肠杆菌单链DNA结合蛋白形成的复合物的光探测三重态磁共振光谱。形成复合物后，蛋白质中色氨酸残基的三重态性质受到重汞原子的扰动，其特征是三重态寿命缩短，并出现强的D + E慢通过光探测磁共振信号。这些表明存在外部重原子效应的特征，为汞化核苷酸碱基与色氨酸残基之间的近距离相互作用提供了直接证据，因为受扰动分子与重原子扰动剂之间需要范德华接触。振幅调制磷光微波双共振技术选择性地显示了重原子扰动的色氨酸三重态的磷光光谱。从空间位阻考虑，强烈暗示通过汞化尿嘧啶碱基与色氨酸的吲哚部分的堆积结构表现出的范德华接触是最合理的相互作用模式，因为汞原子的其他接近方式被2-巯基乙醇与汞的共价连接所阻断。重原子扰动的大小也与汞原子从吲哚芳香平面上方或下方接近π-体系一致，并且至少比边缘接近预期的效应大一个数量级。
