Plum G E, Arscott P G, Bloomfield V A
Department of Biochemistry, University of Minnesota, St. Paul 55108.
Biopolymers. 1990;30(5-6):631-43. doi: 10.1002/bip.360300515.
Electron microscopy is employed to examine DNA aggregates produced by three tripositively charged condensing agents. Spermidine, hexammine cobalt (III), and me8spermidine (in which the amine groups of spermidine are exhaustively methylated) all produce condensates. The predominant form of condensate observed is toroidal; however, me8spermidine produces a large fraction of rodlike condensates. Distributions of toroidal radii and estimated volumes suggest that the size of condensates depends on the condensing agent employed, its concentration, and the time elapsed after addition of condensing agent. While ligand charge seems to be the major factor in predicting condensing power, ligand structure influences the morphology and dimensions of the particles produced. The ability to form hydrogen bonds is not required to promote condensation, since me8spermidine has no NHs. There may be a kinetic barrier to condensation at low me8spermidine concentrations. The relative proportions of toroids and rods may depend on the energetic compensation between bending and binding in cyclic structures, or on rate-limiting formation of sharply bent or kinked regions in rods.
采用电子显微镜检查由三种三价正电荷凝聚剂产生的DNA聚集体。亚精胺、六氨合钴（III）和me8亚精胺（其中亚精胺的胺基被完全甲基化）均能产生凝聚物。观察到的主要凝聚物形式为环形；然而，me8亚精胺产生了很大一部分棒状凝聚物。环形半径和估计体积的分布表明，凝聚物的大小取决于所用的凝聚剂、其浓度以及加入凝聚剂后经过的时间。虽然配体电荷似乎是预测凝聚能力的主要因素，但配体结构会影响所产生颗粒的形态和尺寸。促进凝聚不需要形成氢键的能力，因为me8亚精胺没有NH基团。在低me8亚精胺浓度下，凝聚可能存在动力学障碍。环形和棒状的相对比例可能取决于环状结构中弯曲和结合之间的能量补偿，或者取决于棒状结构中急剧弯曲或扭结区域的限速形成。
