Study On The Hydrolysis Of Biomimetic DPPC Membrane Catalyzed By Phospholipase A₁

In this thesis,the hydrolysis mechanism of the phospholipid（DPPC）biomimetic membrane catalyzed by phospholipase A1 was comprehensively studied via several characterization methods such as sum frequency vibration spectroscopy（SFG）method and confocal fluorescence microscopy（LSCM）method at the molecular scale.During this hydrolysis reaction,different molecules showed their own behavior at the interface due to the interaction force,and some specific domains were formed.This experimental study provides the essential information on revealing the interfacial biochemical process related to the metabolism of the lipids,which is one of the basic building blocks for cells.The interfacial hydrolysis of phospholipids catalyzed by phospholipase A₁（PLA₁）was studied via sum frequency generation（SFG）vibrational spectroscopy and fluorescence microscopy.Both monolayer（PS-dDPPC）and bilayer（dDPPC-DPPC）setups were used to confirm the hydrolysis mechanism.With the help of SFG method,the behavior of different molecules during this hydrolysis reaction was revealed by analyzing the changes of SFG signals from different molecules.Fluorescence co-localization imaging was also used in this research.Through the LSCM method,the dynamic process of different molecular behavior during the hydrolysis reaction and the morphological changes of the entire phospholipid membrane were tracked.The experimental results showed that phospholipase A₁ cleaved the sn-1 ester bond on the glycerol backbone.During the hydrolysis,lysophospholipids,one of the hydrolysis products,were desorbed from the interface into the solution,while the other products,fatty acids,self-organized and accumulated with PLA₁ at the interface to form the PLA₁ induced regions.In this study,an interfacial phospholipid hydrolysis reaction is used as an example to establish an experimental system based on modern optical technology which can characterize the information of interfacial molecules and it provided important experimental data and theoretical basis for exploring and understanding this important biophysical and chemical process of phospholipid hydrolysis.In addition,the hydrophobic PLA₁ induced region can serve as nonspecific binding domains for proteins and may lead to understanding of human vascular diseases from the perspective of this study.