Flach C R, Brauner J W, Mendelsohn R
Department of Chemistry, Newark College of Arts and Sciences, Rutgers University, New Jersey 07102.
Biophys J. 1993 Nov;65(5):1994-2001. doi: 10.1016/S0006-3495(93)81276-1.
External reflection Fourier transform infrared (FT-IR) experiments are reported for insoluble monomolecular films of an equimolar mixture of 1,2-dipalmitoylphosphatidylcholine (DPPC) and 1,2-dipalmitoylphosphatidylserine (DPPS) at the A/W interface as a function of surface pressure and Ca2+ ion presence. The separate components showed a surface pressure-induced conformational ordering of the acyl chains. The conformational ordering occurred more cooperatively for the DPPS. Acyl chain perdeuteration of the DPPC permitted the observation of the response of the individual components in the binary mixture to changes in surface tension and to the presence of Ca2+. Plots of surface pressure versus CH2 or CD2 stretching frequencies were analyzed with a two-state model. At each surface pressure within the two-state region, the fraction of disordered form was the same for each lipid component, suggesting that they are well mixed on the surface. Calcium ion (5 mM in the subphase) produces almost no effect on the pressure-induced acyl chain ordering of the DPPC in a single component film, whereas the same levels of Ca2+ induce acyl chain ordering at all surface pressures in both components of the binary mixture. Thus, unlike the bulk phase mixture of DPPC/DPPS, the binary lipids in this mixed monolayer film appear to retain their miscibility in the presence of Ca2+. Finally, Ca(2+)-induced dehydration of the phosphate group was observed through characteristic frequency shifts in the asymmetric PO2- stretching mode.
报道了在气/水（A/W）界面上，1,2-二棕榈酰磷脂酰胆碱（DPPC）和1,2-二棕榈酰磷脂酰丝氨酸（DPPS）等摩尔混合物的不溶性单分子膜的外反射傅里叶变换红外（FT-IR）实验，该实验是表面压力和Ca2+离子存在情况的函数。单独的组分显示出酰基链的表面压力诱导构象有序化。DPPS的构象有序化发生得更协同。DPPC的酰基链全氘化使得能够观察二元混合物中各组分对表面张力变化和Ca2+存在的响应。用双态模型分析了表面压力与CH2或CD2伸缩频率的关系图。在双态区域内的每个表面压力下，每种脂质组分的无序形式分数相同，这表明它们在表面上混合良好。钙离子（在亚相中为5 mM）对单一组分膜中DPPC的压力诱导酰基链有序化几乎没有影响，而相同水平的Ca2+在二元混合物的两种组分的所有表面压力下都诱导酰基链有序化。因此，与DPPC/DPPS的本体相混合物不同，这种混合单分子层膜中的二元脂质在Ca2+存在下似乎保持其互溶性。最后，通过不对称PO2-伸缩模式的特征频率位移观察到Ca(2+)诱导的磷酸基团脱水。
