A Study On The Interfacial Behavior Of Lipids With Phytosterols And Bovine Serum Albumin

With the continuous renewal of modern experiment technology, interdisciplinary theory and development technology integration and perfection, biology, physics, chemistry, Pharmacology and clinical contacts gradually highlighted and becomes the current topics in the field of science. Especially the study of biomembrane has become more popular on cell biology, biophysics, molecular biology, biomembrane is a supermolecule syetem consisted of lipid, protein and saccharide, which has an important role on substance transportation, energy transformation, signal identification and transduction. Its structure and function have become a hot topic. A large number of studies show that the life activities are inextricably linked with biomembrane.In this paper, we have researched the two respects:(1) Thermodynamic study on the mixed monolayer:The interactions between P-sitosterol and stigmasterol and dipalmitoyl phosphatidycholine (DPPC) in mixed monolayers have been studied by langmuir technique and atomic force microscopy (AFM). The influence of P-sitosterol and stigmasterol effects on properties of DPPC membrane on phase transition from the liquid expanded (LE) to liquid condensed (LC) state were investigated and the condensing and ordering potency of binary monolayers containing β-sitosterol and stigmasterol were thoroughly analyzed. Based on the analysis of mixing values as well as AFM images it was evidenced that the effect of the plant sterol depends on the composition of model membrane. The results show that:It was found that the addition of the plant sterols into model membrane modifies the condensation, ordering and interactions in the system. Moreover, at their higher concentration, Xsterols=0.8, the values of the excess molecular area and excess Gibbs enerqy displayed negative values, which indicate that between molecules in the mixed monolayer exist stronger attraction than in the respective one-component films and suggest β-sitosterol and stigmasterol in the mixed system are the similar effects on its properties. Examination of the excess free energy of mixing reveals an enhanced stability of binary monolayers. At lower content, Xsterols=0.2,0.4suggested stronger attractive interaction between stigmasterol and DPPC, while an intermolecular stronger repulsion interaction between β-sitosterol and DPPC. It shows that stigmasterol was found to modify the properties of model membrane more strongly than β-sitosterol. It reflects that side-chain can reduce packing effectiveness, increased tilt of the molecules with respect to the monolayer plane, and the presence of the double bond reduces the hydrophobicity of the branched hydrocarbon tail of stigmasterol, which could cause strols to have long axis parallel to the interface. The result of AFM supported the theoretic analysis.(2) The interaction between lipid and BSA:The influence of zwitterionic lipid, dipalmitoyl phosphatidylcholine (DPPC), the anionic lipid, dipalmitoylphosph atid yl-serine (DPPS) and protein, bovine serum albumin (BSA) induced the changes of protein conformation, which can change the function of the protein. In this work we have investigated the effect of the penetration of BSA into DPPC and DPPS monolayers and the rearrangement of BSA at the air-water interface. The effect is different for the zwitterionic phospholipid (DPPC) and the anionic phospholipid (DPPS) on an aqueous subphase in the absence and presence of10-8M BSA, which demonstrates that the charge of phospholipid has played a significant role for the interaction between protein and phospholipid. Moreover, the factors influenced the effect are so much, including wait time, pH, and surface pressure. The effect of wait time on the diffusion and rearrangement of BSA is in connection with the adsorption in the compression-expansion cycles. At longer time, the adsorption is stronger, and can decrease the hysteretic phenomena, which can make the protein molecules relax back to the original state. The effect of surface pressure is related to the change in morphology of DPPC/BSA and DPPS/BSA mixed membranes. BSA causes a disappearance of sheet like structures for DPPC/BSA membrane, and causes the change in the size and the number of adsorption for DPPS/BSA.