To determine how different constituents of pulmonary surfactant affect its phase behavior, we measured wide-angle x-ray scattering (WAXS) from oriented bilayers. Samples contained the nonpolar and phospholipids (N&PL) obtained from calf lung surfactant extract (CLSE), which also contains the hydrophobic surfactant proteins, SP-B and SP-C. Mixtures with different ratios of N&PL and CLSE provided the same set of lipids with different amounts of the proteins. At 37 °C, N&PL by itself forms coexisting Lα and Lβ phases. In the Lβ structure, the acyl chains of the phospholipids occupy an ordered array that has melted by 40 °C. This behavior suggests that the Lβ composition is dominated by dipalmitoyl phosphatidylcholine (DPPC), which is the most prevalent component of CLSE. The Lβ chains, however, lack the tilt of the Lβ' phase formed by pure DPPC. At 40 °C, WAXS also detects an additional diffracted intensity, the location of which suggests a correlation among the phospholipid headgroups. The mixed samples of N&PL with CLSE show that increasing amounts of the proteins disrupt both the Lβ phase and the headgroup correlation. With physiological levels of the proteins in CLSE, both types of order are absent. These results with bilayers at physiological temperatures indicate that the hydrophobic surfactant proteins disrupt the ordered structures that have long been considered essential for the ability of pulmonary surfactant to sustain low surface tensions. They agree with prior fluorescence micrographic results from monomolecular films of CLSE, suggesting that at physiological temperatures, any ordered phase is likely to be absent or occupy a minimal interfacial area.

中文翻译：

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抑制肺表面活性物质脂质中 Lα/Lβ 相共存

为了确定肺表面活性剂的不同成分如何影响其相位行为，我们测量了定向双层的广角 X 射线散射 (WAXS)。样品含有从小牛肺表面活性剂提取物 (CLSE) 中获得的非极性和磷脂 (N&PL)，其中还含有疏水性表面活性蛋白 SP-B 和 SP-C。具有不同比例的 N&PL 和 CLSE 的混合物提供了具有不同数量蛋白质的同一组脂质。在 37 °C 时，N&PL 本身形成共存的 Lα 和 Lβ 相。在 Lβ 结构中，磷脂的酰基链占据有序阵列，在 40 °C 时熔化。这种行为表明 Lβ 成分以二棕榈酰磷脂酰胆碱 (DPPC) 为主，它是 CLSE 中最普遍的成分。然而，Lβ 链缺乏 Lβ' 的倾斜度 由纯 DPPC 形成的相。在 40 °C 时，WAXS 还检测到额外的衍射强度，其位置表明磷脂头基之间存在相关性。N&PL 与 CLSE 的混合样本表明，蛋白质数量的增加会破坏 Lβ 相和头部组相关性。对于 CLSE 中蛋白质的生理水平，两种类型的顺序都不存在。这些在生理温度下使用双层的结果表明，疏水性表面活性蛋白破坏了长期以来被认为对肺表面活性剂维持低表面张力的能力至关重要的有序结构。他们同意先前来自 CLSE 单分子薄膜的荧光显微成像结果，表明在生理温度下，