碱性磷酸酶定位方向对DPPC液晶单层膜热力学特性的影响

Orientation of alkaline phosphatase change the thermodynamic characteristics of DPPC liquid crystal monolayer

采用3种不同方法将碱性磷酸酶(AP)添加在DPPC单层膜系统中,从热力学角度研究了AP对DPPC单层膜的影响,旨在从分子水平探讨AP分子与磷脂生物膜的作用机理。结果表明,用共同铺展法和亚相溶解法添加AP后,DPPC单层膜的相变不受影响。在低表面压力下,AP在膜上的定位从长轴与界面平行变为垂直方向,这改变了膜体系中分子间的相互作用力,减小了膜体系的混乱程度,增大了膜体系的能量。而用亚相注入法添加蛋白AP后,DPPC单层膜的相转移变得不明显,在低表面压力下AP分子的定位方向不变。在高表面压力下,AP分子可能被DPPC胶束包裹,并释放到单层膜外,这不仅改变了体系分子间的相互作用力,而且增大了体系的混乱程度,并减小了体系能量。碱性磷酸酶分子的定位方向对其与磷脂膜的相互作用起到至关重要的作用。

In order to investigate the interaction between alkaline phosphate （AP） and phospholipid monolayer on the molecular level,the effect of alkaline phosphate on the DPPC monolayer was studied by thermodynamics in the three different methods of AP addition. The results showed that the phase transition of DPPC monolayer was not affected by AP in the two manners of co-spreading and subphase formation. At low surface pressure, the major axis of AP molecule turns to be parallel to the interface from vertical. The change of AP＇s orientation on the DPPC monolayer influences the interaction force between the molecules, reduces the disorder of the monolayer and increases the energy of system. In contrast, in the method of injection, AP molecules make the phase transition of DPPC monolayer become insignificant. The major axis of AP remains to be parallel to the interface at low surface pressure. However, at high surface pressure, AP molecules might be encased by DPPC micelles and released to the outside of monolayer. It not only changes the intermolecular interaction force but also increases the disorder of DPPC monolayer and decreases the energy of system. Therefore, the orientation of alkaline phosphatase molecule plays a critical role in its interaction with the DPPC monolayer.