Walker Barry W, Manhanke Nathan, Stine Keith J
Department of Chemistry and Biochemistry, University of Missouri - St. Louis, One University Boulevard, Saint Louis, MO 63121, USA.
Biochim Biophys Acta. 2008 Oct;1778(10):2244-57. doi: 10.1016/j.bbamem.2008.06.004. Epub 2008 Jun 13.
The interaction of the glycoalkaloid tomatine with monolayers of a phospholipid (dimyristoylphosphatidylcholine, DMPC), and sphingolipid (egg sphingomyelin), and cholesterol is compared. Using measurements of the surface pressure response as a function of the subphase concentration of tomatine, interfacial binding constants are estimated for mixed monolayers of DMPC and cholesterol and for those of egg sphingomyelin and cholesterol of mole ratio 7:3. The binding constants obtained suggest a stronger interaction of tomatine with DMPC and cholesterol mixed monolayers, reflecting easier displacement of cholesterol from its interaction with DMPC than from its interaction with egg sphingomyelin. Mixtures of tomatine and cholesterol are found to spread directly at the water-air interface and form stable monolayers, suggesting that cholesterol holds tomatine at the interface despite the absence of observed monolayer behavior for tomatine alone. The interaction of tomatine with DMPC and cholesterol monolayers is found to exhibit a pH dependence in agreement with previously reported results for its interaction with liposomes; in particular, the interaction is much less at pH 5 than at pH 7 or pH 9. It is found that while tomatine interacts strongly with monolayers containing sitosterol, it does not interact with monolayers containing sitosterol glucoside. The response of monolayers of varying composition of DMPC and cholesterol to tomatine is also examined. Brewster angle microscopy (BAM) reveals further evidence for formation of suspected islands of tomatine + cholesterol complexes upon interaction with mixed monolayers of lipid and sterol.
比较了糖生物碱番茄碱与磷脂（二肉豆蔻酰磷脂酰胆碱，DMPC）、鞘脂（鸡蛋鞘磷脂）和胆固醇单分子层之间的相互作用。通过测量表面压力响应随番茄碱亚相浓度的变化，估算了DMPC与胆固醇混合单分子层以及摩尔比为7:3的鸡蛋鞘磷脂与胆固醇混合单分子层的界面结合常数。所获得的结合常数表明番茄碱与DMPC和胆固醇混合单分子层之间的相互作用更强，这反映出胆固醇与DMPC的相互作用比与鸡蛋鞘磷脂的相互作用更容易被番茄碱取代。发现番茄碱与胆固醇的混合物可直接在水 - 空气界面铺展并形成稳定的单分子层，这表明尽管单独的番茄碱未观察到单分子层行为，但胆固醇可将番茄碱保持在界面处。发现番茄碱与DMPC和胆固醇单分子层的相互作用表现出pH依赖性，这与先前报道的其与脂质体相互作用的结果一致；特别是，在pH 5时的相互作用比在pH 7或pH 9时小得多。发现虽然番茄碱与含有谷甾醇的单分子层强烈相互作用，但它与含有谷甾醇葡萄糖苷的单分子层不相互作用。还研究了不同组成的DMPC和胆固醇单分子层对番茄碱的响应。布鲁斯特角显微镜（BAM）揭示了与脂质和甾醇混合单分子层相互作用时形成疑似番茄碱+胆固醇复合物岛的进一步证据。
