Panda A K, Hume A, Nag K, Harbottle R R, Petersen N O
Department of Chemistry, Behala College, Kolkata 700 060, India.
Indian J Biochem Biophys. 2003 Apr;40(2):114-21.
Structures of the monolayer films of dipalmitoylphosphatidylcholine (DPPC) mixed with different amounts of cholesterol were studied at air-water interface using surface pressure-area measurements, epifluorescence microscopy and atomic force microscopy (AFM). Pure DPPC, cholesterol or DPPC-cholesterol mixtures were dissolved in organic solvents with a small amount of fluorescently labeled phospholipid probe (NBD-PC) and spread onto the air-water interface. Surface pressure-area isotherms and epifluorescence microscopy of such films at the air-water interface suggested that DPPC undergoes a gas to fluid to condensed phase transition, while cholesterol undergoes a gas to solid-like transition. A shift of the surface pressure-area curve to lower area per molecule was observed when cholesterol was mixed with DPPC. Epifluorescence microscopy showed the formation of spiral shaped domains for mixed monolayers. Increase in cholesterol content abolished domain characteristics possibly due to fluidizing property of cholesterol. AFM measurements of monolayers, transferred onto freshly cleaved mica by Langmuir-Blodgett technique, revealed the alterations caused by cholesterol on the gel and fluid domains of such films. AFM measurements re-established similar trend in domain characteristics as evidenced in epifluorescence microscopy.
利用表面压力-面积测量、落射荧光显微镜和原子力显微镜（AFM），在气-水界面研究了与不同量胆固醇混合的二棕榈酰磷脂酰胆碱（DPPC）单层膜的结构。将纯DPPC、胆固醇或DPPC-胆固醇混合物溶解于含有少量荧光标记磷脂探针（NBD-PC）的有机溶剂中，并铺展在气-水界面上。气-水界面处此类膜的表面压力-面积等温线和落射荧光显微镜表明，DPPC经历了从气态到液态再到凝聚相的转变，而胆固醇经历了从气态到类固态的转变。当胆固醇与DPPC混合时，观察到表面压力-面积曲线向每分子更低面积的方向移动。落射荧光显微镜显示混合单层形成了螺旋形区域。胆固醇含量的增加消除了区域特征，这可能是由于胆固醇的流化特性。通过Langmuir-Blodgett技术转移到新鲜劈开云母上的单层膜的AFM测量揭示了胆固醇对此类膜的凝胶域和流体域所造成的改变。AFM测量重新确立了与落射荧光显微镜中所证明的类似的区域特征趋势。
