Saxena K, Duclos R I, Sripada P K, Shipley G G
Department of Biophysics, Center for Advanced Biomedical Research, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
Biophys J. 2000 Jul;79(1):385-93. doi: 10.1016/S0006-3495(00)76300-4.
After deacylation of bovine brain sulfatide under mild alkaline conditions and reacylation using palmitoyl chloride (, Chem. Phys. Lipids. 34:41-53), the anionic glycosphingolipid N-palmitoyl galactosulfatide (C16:0-GalSulf) has been synthesized. By differential scanning calorimetry (DSC), anhydrous C16:0-GalSulf exhibits an endothermic transition, T(M) = 93 degrees C (DeltaH = 5. 5 kcal/mol C16:0-GalSulf) on heating. With increasing hydration (50 mM sodium phosphate buffer, pH 7.0; 50 mM NaCl), T(M) decreases, reaching a limiting value of 49 degrees C (DeltaH = 8.2 kcal/mol C16:0-GalSulf) at 20 wt% buffer. X-ray diffraction data have been recorded over the hydration range 0-62% at temperatures below (20 degrees C) and above (60 degrees C) T(M). At 20 degrees C, sharp wide-angle reflections at approximately 1/4.4 A(-1), approximately 1/4.1 A(-1), and approximately 1/3.8 A(-1) indicate the presence of an ordered-chain gel phase, whereas at 60 degrees C a broad reflection at 1/4.5 A(-1) characteristic of a melted-chain phase is observed. Lamellar diffraction patterns consistent with the presence of bilayer phases are observed at both temperatures. At 60 degrees C, in the liquid-crystalline L(alpha) phase, the bilayer periodicity increases with hydration, in both water and 100 mM Na(+) buffer. Interestingly, in the gel phase at 20 degrees C, the bilayer periodicity (d = 64 A) is insensitive to hydration (over the range 30-60 wt%) with either water or buffer. The continuous swelling behavior exhibited by the L(alpha) bilayer phase of C16:0-GalSulf is typical of lipids bearing a net negative charge and confirms that the presence of 100 mM Na(+) is insufficient to shield the charge contributed by the sulfate group. In contrast, the lack of continuous swelling behavior of the bilayer gel phase of C16:0-GalSulf is unusual and resembles that of Na(+) soaps. Thus, presumably, alterations in the surface charge characteristics of the C16:0-GalSulf bilayer occur on hydrocarbon chain melting and lead to major changes in lipid hydration.
在温和碱性条件下对牛脑硫脂进行脱酰基反应，并使用棕榈酰氯进行再酰基化反应（《化学与物理脂质》，34:41 - 53）后，合成了阴离子糖鞘脂N - 棕榈酰半乳糖硫脂（C16:0 - GalSulf）。通过差示扫描量热法（DSC），无水C16:0 - GalSulf在加热时呈现吸热转变，T(M) = 93℃（ΔH = 5.5千卡/摩尔C16:0 - GalSulf）。随着水合作用增强（50 mM磷酸钠缓冲液，pH 7.0；50 mM NaCl），T(M)降低，在20 wt%缓冲液时达到极限值49℃（ΔH = 8.2千卡/摩尔C16:0 - GalSulf）。在低于（20℃）和高于（60℃）T(M)的温度下，记录了0 - 62%水合范围内的X射线衍射数据。在20℃时，约1/4.4 Å⁻¹、约1/4.1 Å⁻¹和约1/3.8 Å⁻¹处的尖锐广角反射表明存在有序链凝胶相，而在60℃时，观察到1/4.5 Å⁻¹处的宽反射，这是熔融链相的特征。在两个温度下均观察到与双层相存在一致的层状衍射图案。在60℃的液晶L(α)相中，在水和100 mM Na⁺缓冲液中，双层周期性均随水合作用增加。有趣的是，在20℃的凝胶相中，双层周期性（d = 64 Å）对水合作用（在30 - 60 wt%范围内）不敏感，无论是用水还是缓冲液。C16:0 - GalSulf的L(α)双层相表现出的连续膨胀行为是带有净负电荷脂质的典型特征，并证实100 mM Na⁺的存在不足以屏蔽硫酸根基团贡献的电荷。相比之下，C16:0 - GalSulf双层凝胶相缺乏连续膨胀行为是不寻常的，类似于Na⁺肥皂的情况。因此，推测C16:0 - GalSulf双层的表面电荷特性在烃链熔化时发生改变，并导致脂质水合作用的重大变化。
