Effect of Torsion on Cisplatin-Induced DNA Condensation

We investigate the effect of torsion on DNA condensation with the covalently closed circular DNA as the torsionconstrained system, using an atomic force microscope. It is found that there are two stages in the DNA condensation process under torsional constraint. At the early stage, the low torsion will accelerate DNA condensation by promoting the formation of micro-loops or intersection structures; while at the later stage, the increasing torsion will slow it down by preventing the crosslinking of cisplatin and DNA since the DNA molecule becomes more rigid. Our results show the important role of torsion in DNA condensation and sheds new light on the mechanism for DNA condensation.     

用单分子技术研究抗癌药物顺铂对DNA结构的影响

文章作者用磁镊与原子力显微镜研究了抗癌药物顺铂对单个DNA分子结构的影响.当顺铂浓度较低时,DNA链变得柔软,驻留长度从～52 nm显著缩短到～15 nm;当顺铂浓度较高时,DNA表现出凝聚现象.基于单分子拉伸和原子力显微镜(AFM)成像两方面的实验结果,文章作者提出一个顺铂导致的DNA变软(softening)-成环(looping)-缩短(shortening)-凝聚(condensing)模型(简写为SLSC模型)来解释观察到的DNA凝聚,并认为通过远程交联使DNA形成小环结构是铂类抗癌药物作用的重要特征.     

Effects of pH on Oxaliplatin-Induced Condensation of Single DNA Molecules

By using magnetic tweezers, atomic force microscope and mass spectrometry, we study the effects of pH on oxaliplatin-induced DNA condensation, the DNA persistence length, the amounts of micro-loops and of oxaliplatin bound to DNA. It is found that the DNA condensation degree, the amounts of micro-loops and of oxaliplatin bound to DNA increase with the decrease in the pH value while the DNA persistence length has an opposite behavior. The observed effects may be related to the drug resistance of cancer cells.     

气相色谱-串联质谱法同时测定三七中212种农药残留

建立了气相色谱-串联质谱(GC-MS/MS)同时测定三七中212种农药残留的方法。样品以乙腈-乙酸乙酯(体积比1∶3)提取,经FaPEx-BKT50固相萃取柱净化,待测物采用GC-MS/MS测定,以保留时间和特征离子对定性,外标法定量。结果表明,212种农药在10～200μg/L范围内线性关系良好,相关系数(r²)均大于0.999,检出限(S/N=3)为0.003～0.02 mg/kg,定量下限(S/N=10)为0.01～0.05 mg/kg。在空白样品中进行0.02、0.04、0.1 mg/kg 3个水平的加标回收实验,212种农药的平均回收率为60.0%～121%,相对标准偏差(RSD)为0.90%～31%。该方法简单、灵敏、稳定,可有效去除复杂基体的干扰,各项技术指标均满足国内外农药残留的限量要求,适用于中药材三七中痕量农药的残留测定。     

原子力显微镜观测生物大分子图像的一种处理方法

针对具有复杂结构的生物大分子图像,本文改进了已有的半自动化方法,设计了一种新的算法去消除背景噪声,目的在于能够从生物大分子图像高效准确地提取量化信息.通过利用这种新的处理程序对生物大分子DNA原子力显微镜图像进行了研究,不仅可以对线性构像的DNA图像进行了处理,而且对于具有分支构像复杂DNA图像也能够处理.本文所提出的数字图像处理方法具有普适性,它也可以被应用到其他成像领域. 关键词： 原子力显微镜 数字图像处理 DNA