WATER INDUCED ACTIVITY ON ACTINOMYCIN D DNA INTERCALATION

诱发水活度对插层的影响 用渗透压应激法研究了放线菌素D对DNA的作用 方法：研究方法。得到的结合等温线和结合常数 分光光度滴定表明被排除的溶质 从药物和DNA表面诱导更高的结合水平 复杂的队形。这些测量还揭示了第二个 一类结合位点，在没有 共溶剂，绘制时与水的活度呈线性关系 对数刻度。根据后者，我们已经确定了 药物结合时释放的水分子(NW)是成比例的 至共溶剂的相对分子质量或分子体积。这 结合的水化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释放到主体溶剂中是 在这些存在的情况下观察到更高的ActD嵌入水平 共溶剂。在中等离子强度下，在没有 共溶剂，ActD插层呈现不利的热焓 贡献(HVH=+1.8千卡/摩尔)。我们的假设是 排除共溶剂所产生的熵贡献 可以补偿这一正焓，从而产生更多 有利于有力地捆绑，更有利。为了测试这一点 假设，我们已经测量了量热和范霍夫热 在不同浓度的 蔗糖。初步测量表明，HVH降低 随着蔗糖浓度的增加和由此产生的 溶解NW水分子的熵增加。例如, 在30%(W/V)蔗糖中测得的HVH等于-8.0千卡/摩尔，a值 这通常是在其他药物嵌入DNA时观察到的。 低r比下ActD与DNA结合的量热法测量 蔗糖的存在和缺失与 光谱导出的范特霍夫热焓。这些数据强调 水的重要性，并表明细胞的非理想性 媒介发挥作用 显著控制药物与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.