Zhou J M, Fan Y X, Kihara H, Kimura K, Amemiya Y
National Laboratory of Biomacromolecules, Institute of Biophysics, Academia Sinica, Beijing, China.
FEBS Lett. 1997 Sep 29;415(2):183-5. doi: 10.1016/s0014-5793(97)01120-4.
The denaturation of dimeric creatine kinase (CK) induced by urea and guanidine hydrochloride (GuHCl) has been studied by small angle X-ray scattering (SAXS), which is a direct way to measure the changes in the overall dimensions of a protein molecule. The radii of gyration (Rg) of CK are 29+/-0.4 angstroms in the native state and 46+/-1.5 angstroms in the unfolded state in either 8 M urea or 3 M GuHCl. The transition curves of urea denaturation derived from the Rg values and the zero angle intensity (I(0)) are similar to that from intrinsic fluorescence, indicating that the changes in the molecular shape, the tertiary structure and the dissociation of the subunits proceed simultaneously. In the case of GuHCl-induced denaturation, the dramatic increases both in Rg and in I(0) in 0.3-0.5 M GuHCl suggest clearly that soluble aggregates form at low GuHCl concentrations. The aggregates dissociate and the molecule unfolds at higher GuHCl concentrations. The results suggest that the mechanisms of CK denaturation in urea and in GuHCl are somewhat different and the intermediate in GuHCl denaturation can much more easily form soluble aggregates.
通过小角X射线散射（SAXS）研究了尿素和盐酸胍（GuHCl）诱导的二聚体肌酸激酶（CK）变性，这是一种直接测量蛋白质分子整体尺寸变化的方法。在天然状态下，CK的回转半径（Rg）为29±0.4埃，在8 M尿素或3 M GuHCl中处于未折叠状态时为46±1.5埃。由Rg值和零角度强度（I(0)）得出的尿素变性转变曲线与由内在荧光得出的曲线相似，表明分子形状、三级结构和亚基解离的变化同时发生。在GuHCl诱导变性的情况下，在0.3 - 0.5 M GuHCl中Rg和I(0)都显著增加，这清楚地表明在低GuHCl浓度下形成了可溶性聚集体。在较高的GuHCl浓度下，聚集体解离且分子展开。结果表明，CK在尿素和GuHCl中的变性机制有所不同，并且GuHCl变性中的中间体更容易形成可溶性聚集体。
