WATER INDUCED ACTIVITY ON ACTINOMYCIN D DNA INTERCALATION

研究了诱导水活度对插层的影响， 放线菌素D（actD）对DNA的作用已在渗透胁迫下进行了研究 方法. 结合等温线和常数， 分光光度滴定法指示排除溶质 从药物和DNA表面诱导更高的结合水平， 复杂的形成。 这些测量还揭示了第二个 一类结合位点，在缺乏 共溶剂和线性变化与水的活动时，绘制在 对数刻度 从后者，我们已经确定了数量 药物结合时释放的水分子（NW）， 与共溶剂分子量或分子体积有关。 这 结合时的水合作用和自由能变化之间的联系 溶质分子体积表明， 在药物结合时将NW释放到本体溶剂中是 在这些存在下观察到更高的ActD嵌入水平 共溶剂。 在中等离子强度下， 共溶剂，ActD插层呈现不利的焓 贡献（HvH = +1.8 kcal/mol）。 我们的假设是 排除共溶剂导致的熵贡献 可以补偿这个正焓， 有利的结合力更有利。 为了验证这一 假设，我们已经测量了量热焓和范特霍夫焓 在不同浓度的 蔗糖。 初步测量表明HvH降低 与蔗糖浓度的增加呈线性关系， 溶解NW水分子的熵增加。 比如说， 在30%（W/V）蔗糖中测得的HvH等于-8.0千卡/摩尔， 这通常在其他药物嵌入DNA时观察到。 ActD在低r比下与DNA结合的量热测量， 蔗糖的存在和不存在与 光谱学衍生的范特霍夫光谱。 这些数据强调， 水重要性，并表明细胞的非理想性 媒介发挥 显著控制药物-DNA相互作用的亲和力。

The induced water activity effect upon intercalation of actinomycin D (actD) to DNA has been studied using osmotic stress methods. The binding isotherms and constants obtained by spectrophotometric titration indicate that solutes which are excluded from the drug and DNA surfaces induce higher binding levels upon complex formation. These measurements have also revealed a second class of binding sites which are not accessible in the absence of co-solvents and vary linearly with water activity when plotted on logarithmic scales. From the latter, we have determined the number of water molecules released upon drug binding ( nw) which is proportional to the co-solvent molecular weights or molecular volumes. This linkage between the hydration and free energy changes on binding with solute molecular volumes suggests that the entropic gain upon releasing nw to the bulk solvent upon drug binding is a source for the higher ActD intercalation levels observed in the presence of these co-solvents. At moderate ionic strength and in the absence of co-solvents, ActD intercalation presents an unfavorable enthalpy contribution ( HvH = +1.8 kcal/mol). Our hypothesis is that the entropic contributions resulting from the exclusion of the co-solvent could compensate for this positive enthalpy resulting in more favorable the binding energetically more favorable. To test this hypothesis, we have measured the calorimetric and van't Hoff enthalpy of interacalation in the presence of different concentrations of sucrose. Preliminary measurements indicate that HvH decreases linearly with an increase in sucrose concentration and a resultant increase in entropy of dissolving nw water molecules. For example, the HvH measured in 30% (W/V) sucrose equals - 8.0 kcal/mol, a value that is usually observed for the intercalation of other drugs to DNA. Calorimetric measurements of ActD binding to DNA at low r ratios in the absence and presence of sucrose are consistent with the spectroscopically derived van't Hoff enthalpies. These data emphasize the importance of water and suggest that non-ideality of the cellular medium exerts significant control on the affinity of drug-DNA interactions.