von Nahmen A, Schenk M, Sieber M, Amrein M
Institut für Biochemie, Westfälische Wilhelms-Universität, Münster, Germany.
Biophys J. 1997 Jan;72(1):463-9. doi: 10.1016/S0006-3495(97)78687-9.
The structures formed by a pulmonary surfactant model system of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG), and recombinant surfactant-associated protein C (SP-C) were studied using scanning force microscopy (SFM) on Langmuir-Blodgett films. The films appeared to be phase separated, in agreement with earlier investigations by fluorescence light microscopy. There were smooth polygonal patches of mostly lipid, surrounded by a corrugated rim rich in SP-C. When the films were compressed beyond the equilibrium surface pressure, the protein-rich phase mediated the formation of layered protrusions. The height of these multilamellar structures embodied equidistant steps slightly higher than a DPPC double layer in the gel phase. At the air-water interface too, a high compressibility at low surface tension was indicative of the exclusion of matter. The exclusion process proved to be fully reversible. The present study demonstrates that some of the matter of the model pulmonary surfactant can move in and out of the active monolayer. The SFM images revealed a lipid-protein complex that was responsible for the reversible exclusion of double-layer structures. This mechanism may be important in the natural system too, to keep the surface tension of the alveolar air/water interface constantly low over the range of area encountered upon breathing.
利用扫描力显微镜（SFM）对由二棕榈酰磷脂酰胆碱（DPPC）、二棕榈酰磷脂酰甘油（DPPG）和重组表面活性物质相关蛋白C（SP-C）组成的肺表面活性剂模型系统所形成的结构进行了研究，研究对象为Langmuir-Blodgett膜。这些膜似乎发生了相分离，这与早期荧光显微镜研究结果一致。存在大多为脂质的光滑多边形斑块，周围是富含SP-C的波纹状边缘。当膜被压缩至超过平衡表面压力时，富含蛋白质的相介导了层状突起的形成。这些多层结构的高度呈现出等距台阶，略高于凝胶相中DPPC双层的高度。在气-水界面处，低表面张力下的高压缩性表明有物质被排出。事实证明，排出过程是完全可逆的。本研究表明，模型肺表面活性剂的一些物质能够进出活性单分子层。SFM图像揭示了一种脂质-蛋白质复合物，它导致了双层结构的可逆排出。这种机制在自然系统中可能也很重要，以便在呼吸时遇到的面积范围内，使肺泡气/水界面的表面张力始终保持在较低水平。
