Stellwagen Earle, Lu Yongjun, Stellwagen Nancy C
Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242, USA.
Biochemistry. 2003 Oct 14;42(40):11745-50. doi: 10.1021/bi035203p.
The electrophoretic mobilities and diffusion coefficients of single- and double-stranded DNA molecules up to 50,000 bases or base pairs in size have been analyzed, using mobilities and diffusion coefficients either measured by capillary electrophoresis or taken from the literature. The Einstein equation suggests that the electrophoretic mobilities (mu) and diffusion coefficients (D) should be related by the expression mu/D = Q/k(B)T, where Q is the charge of the polyion (Q = ze(o), where z is the number of charged residues and e(o) is the fundamental electronic charge), k(B) is Boltzmann's constant, and T is the absolute temperature. If this equation were true, the ratio mu/zD should be a constant equal to e(o)/k(B)T (39.6 V(-1)) at 20 degrees C. However, the ratio mu/zD decreases with an increase in molecular weight for both single- and double-stranded DNAs. The mobilities and diffusion coefficients are better described by the modified Einstein equation mu/N(m)D = e(o)/k(B)T, where N is the number of repeat units (bases or base pairs) in the DNA and m is a constant equal to the power law dependence of the diffusion coefficients on molecular weight. The average value of the ratio mu/N(m)D is 40 +/- 4 V(-1) for 36 single- and double-stranded DNA molecules of different sizes, close to the theoretically expected value. The generality of the modified Einstein equation is demonstrated by analyzing literature values for sodium polystyrenesulfonate (PSS). The average value of the ratio mu/N(m)D is 35 +/- 6 V(-1) for 14 PSS samples containing up to 855 monomers.
我们利用通过毛细管电泳测量或从文献中获取的迁移率和扩散系数，分析了大小达50,000个碱基或碱基对的单链和双链DNA分子的电泳迁移率和扩散系数。爱因斯坦方程表明，电泳迁移率（μ）和扩散系数（D）应满足表达式μ/D = Q/k(B)T，其中Q是聚离子的电荷（Q = ze(o)，z是带电残基的数量，e(o)是基本电荷），k(B)是玻尔兹曼常数，T是绝对温度。如果该方程成立，那么在20℃时，μ/zD的比值应是一个常数，等于e(o)/k(B)T（39.6 V(-1)）。然而，对于单链和双链DNA，μ/zD的比值均随分子量的增加而降低。迁移率和扩散系数用修正的爱因斯坦方程μ/N(m)D = e(o)/k(B)T能更好地描述，其中N是DNA中重复单元（碱基或碱基对）的数量，m是一个常数，等于扩散系数对分子量的幂律依赖关系。对于36个不同大小的单链和双链DNA分子，μ/N(m)D比值的平均值为40±4 V(-1)，接近理论预期值。通过分析聚苯乙烯磺酸钠（PSS）的文献值，证明了修正爱因斯坦方程的通用性。对于14个含有多达855个单体的PSS样品，μ/N(m)D比值的平均值为35±6 V(-1)。
