Swanson J E, Feigenson G W
Section of Biochemistry, Cornell University, Ithaca, New York 14853.
Biochemistry. 1990 Sep 11;29(36):8291-7. doi: 10.1021/bi00488a013.
A simple model system is described that allows measurement of equilibrium Ca2+ binding to multilamellar vesicle mixtures of palmitoyloleoylphosphatidylserine (P,O-PS) and dimyristoleoylphosphatidylcholine (MO,MO-PC). The constraint of the chemical equilibrium among aqueous Ca2+, hydrated P,O-PS/MO,MO-PC, and Ca(PS)2, together with measurements of the Ca2+ concentration in equilibrium with defined PS/PC ratios, enables the determination of the thermodynamic activity of the lipids. The activity coefficient of dilute P,O-PS in PC is analyzed in terms of the partial molal free energy to transfer P,O-PS from an environment of PS to an environment of PC. This study of P,O-PS/MO,MO-PC, by comparison with the earlier study of P,O-PS/P,O-PC [Feigensen, G.W. (1989) Biochemistry 20, 1270-1278], reveals that the excess partial molal free energy to transfer P,O-PS from P,O-PS to P,O-PC is -0.7 kcal mol-1. This free energy change arises in part from the favorable transfer of the negatively charged phosphoserine headgroup from an environment of negative charges to an environment of zwitterions. The contribution of acyl chain mismatch to the partial molal free energy to transfer P,O-PS from P,O-PS to MO,MO-PC is found to be approximately +0.7 kcal mol-1. This value is much larger than that of the excess partial molal free energy of mixing in isotropic solutions of linear hydrocarbons that differ in chain length or unsaturation.
本文描述了一个简单的模型系统，该系统可用于测量钙离子与棕榈酰油酰磷脂酰丝氨酸（P，O-PS）和二肉豆蔻酰磷脂酰胆碱（MO，MO-PC）的多层囊泡混合物的平衡结合。水相钙离子、水合P，O-PS/MO，MO-PC和Ca(PS)2之间的化学平衡限制，以及与定义的PS/PC比率平衡时钙离子浓度的测量，使得能够确定脂质的热力学活度。根据将P，O-PS从PS环境转移到PC环境的偏摩尔自由能，分析了PC中稀释的P，O-PS的活度系数。通过与早期对P，O-PS/P，O-PC的研究[Feigensen，G.W.（1989年）生物化学20，1270 - 1278]进行比较，对P，O-PS/MO，MO-PC的这项研究表明，将P，O-PS从P，O-PS转移到P，O-PC的过量偏摩尔自由能为-0.7千卡/摩尔。这种自由能变化部分源于带负电荷的磷酸丝氨酸头部基团从负电荷环境向两性离子环境的有利转移。发现酰基链错配对将P，O-PS从P，O-PS转移到MO，MO-PC的偏摩尔自由能的贡献约为+0.7千卡/摩尔。该值远大于链长或不饱和度不同的线性烃各向同性溶液中混合的过量偏摩尔自由能的值。
