Boggs J M, Koshy K M, Rangaraj G
Department of Biochemistry, Hospital for Sick Children, Toronto, Canada.
Biochim Biophys Acta. 1988 Mar 3;938(3):361-72. doi: 10.1016/0005-2736(88)90134-4.
Cerebroside sulfate (galactosylceramide I3-sulfate) containing alpha-hydroxy lignoceric acid (C24:0h-CBS), nervonic acid (C24:1-CBS), or hexacosanoic acid (C26:0-CBS) was prepared by a semi-synthetic procedure and studied by differential scanning calorimetry. The phase behavior of these species in 2 M KCl was compared to that of shorter chain length hydroxy and non-hydroxy fatty acid species reported earlier. All three of the new lipids undergo metastable phase behavior similar but not identical to the other species. In addition, the metastable phase behavior of all of the non-hydroxy fatty acid species was found to be more complex than previously thought, with several phases of high transition temperatures and enthalpies possible. Fatty acid hydroxylation inhibits the transition from the metastable to some of the more stable phases. It also significantly increases the phase transition temperatures of both the metastable and stable phases indicating that it contributes to the hydrogen bonding network formed between the lipid molecules and helps overcome the lateral repulsive effect of the negatively charged sulfate. The C-15 cis double bond significantly lowers the temperature and enthalpy of the phase transition indicating that it increases the lateral separation of the lipid molecules and decreases the intermolecular hydrogen bonding interactions. However, it does not prevent formation of a more stable phase. By comparing the effect of various structural modifications reported here and earlier it could be concluded that fatty acid chain length has little effect on the phase transition temperature and enthalpy. This suggests that the forces between the lipid molecules may be dominated by head group interactions rather than interactions between the lipid chains. However, fatty acid chain length has a significant effect on the tendency of the hydroxy fatty acid species to form the more stable phase. The ease of formation of the stable phase increases with increase in chain length. Thus an increase in chain length helps overcome the kinetic barrier to stable phase formation presented by hydroxylation of the fatty acid.
通过半合成方法制备了含有α-羟基二十四烷酸（C24:0h-CBS）、神经酸（C24:1-CBS）或二十六烷酸（C26:0-CBS）的硫酸脑苷脂（半乳糖神经酰胺I3-硫酸盐），并采用差示扫描量热法进行了研究。将这些物质在2M KCl中的相行为与之前报道的较短链长羟基和非羟基脂肪酸物质的相行为进行了比较。所有这三种新脂质都表现出亚稳相行为，与其他物质相似但不完全相同。此外，发现所有非羟基脂肪酸物质的亚稳相行为比以前认为的更复杂，可能存在几个具有高转变温度和焓的相。脂肪酸羟基化抑制了从亚稳相到一些更稳定相的转变。它还显著提高了亚稳相和稳定相的相变温度，这表明它有助于脂质分子之间形成氢键网络，并有助于克服带负电荷的硫酸盐的侧向排斥作用。C-15顺式双键显著降低了相变的温度和焓，这表明它增加了脂质分子的侧向间距，并减少了分子间氢键相互作用。然而，它并不能阻止更稳定相的形成。通过比较此处和之前报道的各种结构修饰的影响，可以得出结论，脂肪酸链长度对相变温度和焓的影响很小。这表明脂质分子之间的作用力可能主要由头部基团相互作用而非脂质链之间的相互作用主导。然而，脂肪酸链长度对羟基脂肪酸物质形成更稳定相的倾向有显著影响。稳定相形成的难易程度随链长度的增加而增加。因此，链长度的增加有助于克服脂肪酸羟基化所带来的稳定相形成的动力学障碍。
