水-卵磷脂有序体中的两个热力学常数

卵磷脂(PC)是一种两亲性分子,在水中当超过临界胶束浓度(cmc)以后,呈现一种既有流动性又有有序性的溶致液晶态.它又是脂类生物膜的主要成分,生物物理工作者也常用卵磷脂与水等形成的有序体作为模拟生物膜来研究生物膜的性质.ATP 在生物体中是十分重要的能量传递者,能与许多金属离子结合.Ca~(2+)通过“钙泵”实现跨膜输运.体内碳酸钙等含钙物质的过剩积累会产生各种结石病.了解Ca~(2+)-ATP 在水-卵磷脂有序体中的生成常数K 的变化无疑是有意义的.Mohan 和Rechnitz 已报导了在水溶液中Ca-ATP 生成常数的测定.Amin 等人阐述了胶束中化学反应对生物学的重要意义.Fendler 等人对胶束催化作用有详细沦述.但是前人都未报导当卵磷脂在水中形成有序体时对Ca-ATP 的生成常数

TWO THERMODYNAMIC CONSTANTS IN THE LECITHIN-H_2O ORDER SYSTEM

Association constants of the complexes CaATP~(2-) and Ca_2ATP, K_1, K_2 and the product of solubility of CaCO_3, K_(sp), in the lecithin-water order system (PC-H_2O) have been measured by potentionmeter using a calcium ion selection membrance electrode. We have observed that formation constant of the complex CaATP~(2-), K_1, in the PC-H_2O order system is larger about an order of magnilude than K_1 in the H_2O, and K_1 (PC-H_2O) increases with the concentration of phospholipid in the PC-H_2O system. But the rate of increase of the K_1(PC-H_2O) is reduced with the increase of the concentration of the lecithin beyend(cmc). However, the formation constant of Ca_2ATP, K_2, does not change obviously in the process of increasing PC]. When PC]>cmc], the K_(sp)(PC-H_2O) of CaCO_3 in the PC-H_2O system is larger than K_(sp)(H_2O) of CaCO_3 in the water. It illustrates that the solubility of CaCO_3 is increased in the liguid crystal order system.It is expected that the liquid crystal state in biological body is favorable for the absorbtion of calcium.