小球状蛋白质上的旋转摩擦：介电和流体动力学效应的组合
Rotational friction on small globular proteins: Combined dielectric and hydrodynamic effect
摘要：
已知蛋白质和大分子上的旋转摩擦至少来自两个不同的来源-流体动力学（由于粘度）和介电摩擦（由于极性相互作用）。在现有的理论方法中，后者的影响是以{ \it ad hoc}方式考虑的，通过增加蛋白质的尺寸并添加水合层。本文采用广义任意电荷分布模型（其中电荷由量子化学计算得到）计算了蛋白质表面的转动介电摩擦（$ζ_{hyd}^{stick}$），并采用Harding [S. E. Harding，Comp. Biol. Med. { \bf 12}，75（1982）]。流体动力学摩擦的计算仅用蛋白质的干体积（无水合层）进行。我们发现，通过对$ζ_{DF}$和$ζ_{hyd}^{stick}$求和获得的总摩擦力与实验结果具有合理的一致性，即，$ζ_{exp} \approx ζ_{DF} + ζ_{hyd}^{stick}$。
英文摘要：
Rotational friction on proteins and macromolecules is known to derive contributions from at least two distinct sources -- hydrodynamic (due to viscosity) and dielectric friction (due to polar interactions). In the existing theoretical approaches, the effect of the latter is taken into account in an {\it ad hoc} manner, by increasing the size of the protein with the addition of a hydration layer. Here we calculate the rotational dielectric friction on a protein ($ζ_{DF}$) by using a generalized arbitrary charge distribution model (where the charges are obtained from quantum chemical calculation) and the hydrodynamic friction with stick boundary condition, ($ζ_{hyd}^{stick}$) by using the sophisticated theoretical technique known as tri-axial ellipsoidal method, formulated by Harding [S. E. Harding, Comp. Biol. Med. {\bf 12}, 75 (1982)]. The calculation of hydrodynamic friction is done with only the dry volume of the protein (no hydration layer). We find that the total friction obtained by summing up $ζ_{DF}$ and $ζ_{hyd}^{stick}$ gives reasonable agreement with the experimental results, i.e., $ζ_{exp} \approx ζ_{DF} + ζ_{hyd}^{stick}$.
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