Dasgupta D, Auld D S, Goldberg I H
Biochemistry. 1985 Dec 3;24(25):7049-54. doi: 10.1021/bi00346a004.
The spectra of neocarzinostatin (NCS) chromophore during its reversible association with poly(dA-dT).poly(dA-dT) [poly(dA-dT)] were recorded (at intervals of 17 ms or more) by a cryospectroscopic method. Examination of the spectral changes of a drug during its interaction with DNA has not been previously reported. Such studies indicate binding of chromophore to poly(dA-dT) is a two-step process in which the spectral properties of the intermediate poly(dA-dT). NCS chromophore species closely resemble those of the final equilibrium species. On the basis of cryokinetic studies (at single wavelengths) carried out at low temperature (2 degrees C), the following proposed mechanism of the DNA-drug (PD) interaction was quantitated: (Formula: see text). In analogy with the other reports on the kinetics of drug-DNA interaction, (PD)I and (PD)II could represent externally bound and intercalated complexes, respectively. However, since the spectra of (PD)I and (PD)II are closely similar, it can also be proposed that (PD)I and (PD)II represent two forms of an intercalated complex. The rate and equilibrium constant for each step were determined by examining the kinetics of the forward and reverse reactions. This was accomplished by determining the polynucleotide concentration dependence of the apparent fast and slow first-order rate constants observed during a double-exponential increase in transmittance (at 330 nm) associated with the binding and the apoprotein-induced dissociation rate constant of the chromophore from poly(dA-dT). The opportunity to use apoprotein, instead of a detergent, to follow the kinetics of the reverse reaction provides a novel approach to these studies.(ABSTRACT TRUNCATED AT 250 WORDS)
采用低温光谱法记录了新制癌菌素（NCS）发色团与聚（dA-dT）·聚（dA-dT）[聚（dA-dT）]可逆结合过程中的光谱（间隔17毫秒或更长时间）。此前尚未有关于药物与DNA相互作用过程中光谱变化的研究报道。此类研究表明，发色团与聚（dA-dT）的结合是一个两步过程，其中间体聚（dA-dT）·NCS发色团物种的光谱特性与最终平衡物种的光谱特性非常相似。基于在低温（2摄氏度）下进行的低温动力学研究（在单一波长下），对DNA-药物（PD）相互作用的以下拟议机制进行了定量：（公式：见原文）。与其他关于药物-DNA相互作用动力学的报道类似，（PD）I和（PD）II可能分别代表外部结合和插入复合物。然而，由于（PD）I和（PD）II的光谱非常相似，也可以提出（PD）I和（PD）II代表插入复合物的两种形式。通过研究正向和反向反应的动力学来确定每一步的速率和平衡常数。这是通过确定在与发色团与聚（dA-dT）结合以及脱辅基蛋白诱导发色团从聚（dA-dT）解离相关的双指数透射率增加（在330纳米处）过程中观察到的表观快速和慢速一级速率常数的多核苷酸浓度依赖性来实现的。使用脱辅基蛋白而非去污剂来跟踪反向反应动力学，为这些研究提供了一种新方法。（摘要截短于250字）
