盐效应对DNA大分子构象的影响

THE EFFECT OF SALT ON CONFORMATION OF DNA MOLECULE

用CD光谱监测了Micrococcus luteus DNA在不同MgCl_2浓度下[θ]值的变化,发现随着MgCl_2浓度的增加,在275nm处其[θ]值减少;而在220—250nm处,其负[θ]值加大.这个结果表明DNA大分子在空间上趋于缩拢.在同样条件下也用紫外光谱进行了监测,发现随着MgCl_2浓度的增加,在260nm处有明显的减色效应出现,这便又进一步印证了上述结果.而又用Batch-2107微量热计进行了热力学上的研究,结果表明在上述条件下,随着DNA大分子在空间上缩拢程度的加大,则伴有较高的释热值.这便从热力学的角度进一步佐证了这样的结果:随着MgCl_2浓度的增加,使溶液中的DNA大分子在空间上产生明显的缩拢现象.同时,所有上述测定结果都一致表明:这种DNA大分子构象变化过程是时间依赖的,约持续10分钟.

The CD spectra of Micrococcus luteus DNA at UV region under different concentration of MgCl2 has been measured. The[θ] value decreases at 275nm with increasing of MgCl2 concentration; The -[θ] value increases at 220 -250nm with increasing of MgCl2 concentration. This Result shows that the M. L.DNA molecule tends to shrink in space. The UV spectra of M.L.DNA at the same condition of MgCl2 concentration shows that a hypochromicity happens at 260nm with increasing concentration of MgCl2. The Heat evolved of M.L.DNA under different MgCl2 concentration has been measured with LKB Batch-2107 Microcalorimeter at 25℃. The result of micro microcaloric measurement shows that the heat evolved of M.L.DNA increases with increasing salt concentration. All of these measuements are dependent on time which is taken 10 minutes.