Orientation of alkaline phosphatase change the thermodynamic characteristics of DPPC liquid crystal monolayer
WANG Juan1,2, SUN Runguang2*, HAO Changchun2, MIAO Zongcheng1,MA Yahong3,4, LI Tuo1, XIN Duqiang1
(1 Department of Applied Statistics and Science, Xijing University, Xi′an 710123, Shaanxi, China; 2 School of Physics and Information Technology, Shaanxi Normal University, Xi′an 710119, Shaanxi, China;3 Department of Information Engineering, Xijing University, Xi′an 710123, Shaanxi, China;4 Department of Radiation Medicine, Fourth Military Medical University,Xi′an 710032, Shaanxi, China)
Abstract:
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.
KeyWords:
soluble protein; phase transition; intermolecular interaction force; disorder; DPPC monolayer
