Sömjen G J, Lipka G, Schulthess G, Koch M H, Wachtel E, Gilat T, Hauser H
Department of Gastroenterology, Souraski Medical Center, Ichilov Hospital, Tel-Aviv, Israel.
Biophys J. 1995 Jun;68(6):2342-9. doi: 10.1016/S0006-3495(95)80416-9.
The behavior of mixed bile salt micelles consisting of sodium taurocholate, egg phosphatidylcholine, and cholesterol has been studied by ESR spin labeling and synchrotron x-ray scattering. Consistent with published phase diagrams, pure and mixed bile salt micelles have a limited capacity to incorporate and, hence, solubilize cholesterol. Excess cholesterol crystallizes out, a process that is readily detected both by ESR spin labeling using 3-doxyl-5 alpha-cholestane as a probe for cholesterol and synchrotron x-ray scattering. Both methods yield entirely consistent results. The crystallization of cholesterol from mixed bile salt micelles is indicated by the appearance of a magnetically dilute powder spectrum that is readily detected by visual inspection of the ESR spectra. Both the absence of Heissenberg spin exchange and the observation of a magnetically dilute powder spectrum provide evidence for the spin label co-crystallizing with cholesterol. In mixed bile salt micelles containing egg phosphatidylcholine, the solubility of cholesterol is increased as detected by both methods. With increasing content of phosphatidylcholine and increasing mole ratio cholesterol/phosphatidylcholine, the anisotropy of motion of the spin probe increases. The spin label 3-doxyl-5 alpha-cholestane is a useful substitute for cholesterol provided that it is used in dilute mixtures with excess cholesterol: the cholesterol/spin label mole ratio in these mixtures should be greater than 100. Despite the structural similarity between the two compounds, there are still significant differences in their physico-chemical properties. These differences come to the fore when cholesterol is totally replaced by the spin-label: 3-doxyl-5a-cholestane is significantly less soluble in bile salt and mixed bile salt micelles than cholesterol and, in contrast with cholesterol, it interacts only very weakly, if at all,with phosphatidylcholine. The potential of the ESR method for detecting cholesterol crystal growth in human bile is discussed.
通过电子自旋共振（ESR）自旋标记和同步加速器X射线散射研究了由牛磺胆酸钠、蛋黄卵磷脂和胆固醇组成的混合胆盐微团的行为。与已发表的相图一致，纯胆盐微团和混合胆盐微团结合并溶解胆固醇的能力有限。过量的胆固醇会结晶析出，这一过程可通过使用3-羟基-5α-胆甾烷作为胆固醇探针的ESR自旋标记以及同步加速器X射线散射轻易检测到。两种方法得到的结果完全一致。混合胆盐微团中胆固醇的结晶表现为磁稀释粉末谱的出现，通过对ESR谱的目视检查很容易检测到。海森堡自旋交换的缺失以及磁稀释粉末谱的观察都为自旋标记与胆固醇共结晶提供了证据。在含有蛋黄卵磷脂的混合胆盐微团中，两种方法均检测到胆固醇的溶解度增加。随着卵磷脂含量的增加以及胆固醇/卵磷脂摩尔比的增加，自旋探针运动的各向异性增加。自旋标记物3-羟基-5α-胆甾烷是胆固醇的一种有用替代物，前提是它用于与过量胆固醇的稀混合物中：这些混合物中胆固醇/自旋标记物的摩尔比应大于100。尽管这两种化合物在结构上相似，但它们的物理化学性质仍存在显著差异。当胆固醇完全被自旋标记物取代时，这些差异就凸显出来：3-羟基-5α-胆甾烷在胆盐和混合胆盐微团中的溶解度明显低于胆固醇，并且与胆固醇不同，它与卵磷脂的相互作用非常弱（如果有相互作用的话）。本文讨论了ESR方法检测人胆汁中胆固醇晶体生长的潜力。
