| Summary: | 碩士 === 國立中央大學 === 物理研究所 === 95 === The main components of cell membranes is lipid.In this investigation, we use the lipide vesicles --SUV (small unilamellar vesicle, with size around 30nm) with POPC/POPG(3/1) mixture, that have negative surface charge as our membrane models to study the thermaldynamics of antimicrobial peptide(called peptide, that have positive charge) binding to membranes.
In this investigation, the solution of antimicrobial peptide (Ma2-amide, purified from frog) were titrated by a series of SUV solution, to study the binding of lipid and peptide at 30°C and pH=7.4 environment. Circular dichroism (CD) can measure the spectrum of peptide binding in membrane and free in buffer, from this binding isotherm to analyze the free energy change △G from binding. In isothermal titration calorimetry (ITC), the binding enthalpy ΔH will measure, and according to binding isotherm, we can get the binding enthalpy per binding peptide.
Peptides binding to membrane have two types of many-body effect, (1) membrane thinning effect, and (2) membrane surface charge neutralized effect. Both of two will reduce ΔH (being less negative) as bound peptides increase. But in this L into P experiment, ΔH decrease much faster then the many-body effect. There are other exothermic reactions occur – binding peptide transfer to new SUV in L into P experiment.
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