Ramstedt B, Slotte J P
Department of Biochemistry and Pharmacy, Abo Akademi University, FIN 20521 Turku, Finland.
Biophys J. 1999 Sep;77(3):1498-506. doi: 10.1016/S0006-3495(99)76997-3.
In this study stereochemically pure d-erythro-sphingomyelins (SMs) with either 16:0 or 18:1(cisDelta9) as the N-linked acyl-chain were synthesized. Our purpose was to examine the properties of these sphingomyelins and acyl-chain matched racemic (d-erythro/l-threo) sphingomyelins in model membranes. Liquid-expanded d-erythro-N-16:0-SM in monolayers was observed to pack more densely than the corresponding racemic sphingomyelin. Cholesterol desorption to beta-cyclodextrin was significantly slower from d-erythro-N-16:0-SM monolayers than from racemic N-16:0-SM monolayers. Significantly more condensed domains were seen in cholesterol/d-erythro-N-16:0-SM monolayers than in the corresponding racemic mixed monolayers, when [7-nitrobenz-2-oxa-1, 3-diazol-4-yl]phosphatidylcholine was used as a probe in monolayer fluorescence microscopy. With monolayers of N-18:1-SMs, both the lateral packing densities (sphingomyelin monolayers) and the rates of cholesterol desorption (mixed cholesterol/sphingomyelin monolayers) was found to be similar for d-erythro and racemic sphingomyelins. The phase transition temperature and enthalpy of d-erythro-N-16:0-SM in bilayer membranes were slightly higher compared with the corresponding racemic sphingomyelin (41.1 degrees C and 8.4 +/- 0.4 kJ/mol, and 39.9 degrees C and 7.2 +/- 0.2 kJ/mol, respectively). Finally, d-erythro-sphingomyelins in monolayers (both N-16:0 and N-18:1 species) were not as easily degraded at 37 degrees C by sphingomyelinase (Staphylococcus aureus) as the corresponding racemic sphingomyelins. We conclude that racemic sphingomyelins differ significantly in their biophysical properties from the physiologically relevant d-erythro sphingomyelins.
在本研究中，合成了N-连接酰基链为16:0或18:1（顺式Δ9）的立体化学纯的d-赤藓糖型鞘磷脂（SMs）。我们的目的是研究这些鞘磷脂以及酰基链匹配的外消旋（d-赤藓糖型/l-苏阿糖型）鞘磷脂在模型膜中的性质。观察到单层中液体扩张的d-赤藓糖型-N-16:0-SM比相应的外消旋鞘磷脂堆积更紧密。从d-赤藓糖型-N-16:0-SM单层向β-环糊精的胆固醇解吸明显比从外消旋N-16:0-SM单层慢。当[7-硝基苯并-2-恶唑-1,3-二氮杂环丁烷-4-基]磷脂酰胆碱用作单层荧光显微镜的探针时，在胆固醇/d-赤藓糖型-N-16:0-SM单层中观察到的凝聚域明显比相应外消旋混合单层中的多。对于N-18:1-SMs的单层，发现d-赤藓糖型和外消旋鞘磷脂的侧向堆积密度（鞘磷脂单层）和胆固醇解吸速率（胆固醇/鞘磷脂混合单层）相似。双层膜中d-赤藓糖型-N-16:0-SM的相变温度和焓与相应的外消旋鞘磷脂相比略高（分别为41.1℃和8.4±0.4kJ/mol，以及39.9℃和7.2±0.2kJ/mol）。最后，单层中的d-赤藓糖型鞘磷脂（N-16:0和N-18:1两种）在37℃下不像相应的外消旋鞘磷脂那样容易被鞘磷脂酶（金黄色葡萄球菌）降解。我们得出结论，外消旋鞘磷脂在生物物理性质上与生理相关的d-赤藓糖型鞘磷脂有显著差异。
