Taneva S, Keough K M
Department of Biochemistry, Memorial University of Newfoundland, St. John's, Canada.
Biochemistry. 1997 Jan 28;36(4):912-22. doi: 10.1021/bi9623542.
Cholesterol is a substantial component of pulmonary surfactant (approximately 8 wt % or approximately 14 mol % of surfactant lipids). This study investigated the effect of cholesterol on the way in which hydrophobic SP-B and SP-C modulated the adsorption of lipid into the air-water interface and their respreading from collapsed phase produced on overcompression of the surface film. The properties of binary spread monolayers of SP-B or SP-C plus cholesterol (CH) were consistent with miscibility between the hydrophobic proteins and the sterol. Results from surface pressure versus area measurements at 23 degrees C on spread monolayers of dipalmitoylphosphatidylcholine (DPPC) plus SP-B in the presence of 8 wt % cholesterol implied that CH did not significantly affect the properties of the films of SP-B/(DPPC/CH) compared to those of binary SP-B/DPPC monolayers. In contrast, CH appeared to enhance the mixing of SP-C with DPPC/CH in ternary SP-C/(DPPC/CH) films compared to the miscibility of SP-C with DPPC in the SP-C/DPPC films. It is estimated that about 10 wt % SP-C might remain in the SP-C/(DPPC/CH) monolayers compressed to high surface pressures of about 72 mN/m, whereas SP-C at concentrations of > or = 5 wt % was squeezed out at pi approximately 50 mN/m from SP-C/DPPC films without cholesterol. Cholesterol reduced the stability of the films of SP-B/(DPPC/CH) and SP-C/(DPPC/CH) when they had been compressed to pi approximately 72 mN/m, in contrast to films of SP-B/DPPC and SP-C/DPPC which exhibited a relatively slow relaxation from the collapse pressure of 72 mN/m. Dynamic cyclic compression beyond collapse of SP-B/(DPPC/CH) and SP-C/(DPPC/CH) monolayers showed that cholesterol diminished their postcollapse respreading compared to the respreading of the protein/DPPC films without cholesterol. Cholesterol, at 8 wt %, inhibited the rate of adsorption to the air-water interface at 35 degrees C of aqueous dispersions of DPPC containing 2.5 or 5 wt % SP-B or SP-C. The results suggest that cholesterol has an apparent negative influence on the surfactant surface properties, which are generally considered to be important in surfactant function, although increasing protein concentrations can counteract some of the negative influences.
胆固醇是肺表面活性剂的重要组成部分（约占表面活性剂脂质的8 wt%或约14 mol%）。本研究调查了胆固醇对疏水性表面活性蛋白B（SP-B）和表面活性蛋白C（SP-C）调节脂质吸附到气-水界面以及它们从表面膜过度压缩产生的塌陷相中再铺展方式的影响。SP-B或SP-C与胆固醇（CH）的二元铺展单分子层的性质与疏水性蛋白质和甾醇之间的混溶性一致。在23摄氏度下，对含有8 wt%胆固醇的二棕榈酰磷脂酰胆碱（DPPC）加SP-B的铺展单分子层进行表面压力与面积测量的结果表明，与二元SP-B/DPPC单分子层相比，CH对SP-B/(DPPC/CH)膜的性质没有显著影响。相比之下，与SP-C/DPPC膜中SP-C与DPPC的混溶性相比，CH似乎增强了三元SP-C/(DPPC/CH)膜中SP-C与DPPC/CH的混合。据估计，在压缩至约72 mN/m的高表面压力时，约10 wt%的SP-C可能会保留在SP-C/(DPPC/CH)单分子层中，而在没有胆固醇的情况下，浓度≥5 wt%的SP-C在π约为50 mN/m时会从SP-C/DPPC膜中挤出。与表现出从72 mN/m的塌陷压力相对缓慢松弛的SP-B/DPPC和SP-C/DPPC膜相比，当SP-B/(DPPC/CH)和SP-C/(DPPC/CH)膜被压缩至π约为72 mN/m时，胆固醇降低了它们的稳定性。对SP-B/(DPPC/CH)和SP-C/(DPPC/CH)单分子层塌陷后的动态循环压缩表明，与不含胆固醇的蛋白质/DPPC膜的再铺展相比，胆固醇减少了它们塌陷后的再铺展。8 wt%的胆固醇在35摄氏度下抑制了含有2.5或5 wt% SP-B或SP-C的DPPC水分散体吸附到气-水界面的速率。结果表明，胆固醇对表面活性剂的表面性质有明显的负面影响，而表面活性剂的表面性质通常被认为对表面活性剂功能很重要，尽管增加蛋白质浓度可以抵消一些负面影响。
