The Interaction Between Catechin And Plasma Protein And The Antioxidant Effect Of Complex

As the important components of human nutrition and functional food,catechins have strong antioxidant properties which can prevent many diseases.However,the health-promoting functions of bioactive catechins in vitro and in vivo are often limited by their low stability.Heme is a protein complement which performs important physiological functions in vivo.However,heme could catalyze the generations of active free radicals which cause severe damage to tissues and cells.Plasma proteins in vivo often play a dominant role in controlling the pharmacokinetics,stability and toxicity of bioactive small molecules.Therefore,it is of great interest to develop the carriers that simultaneously contain several bioactive compounds,thus providing multiple benefits to these different compounds.The main content of this thesis was divided into two parts:1.Firstly,the interactions between Bovine Serum Albumin(BSA)and four catechins(i.e.Epigallocatechin Gallate(EGCG),Epigallocatechin(EGC),Epicatechin Gallate(ECG),Epicatechin(EC))were investigated.The fluorescence spectroscopy and molecular docking technology was applied.The binding parameters were calculated from the Stern-Volmer equation.The results showed that the affinities of BSA to these catechins were in the order of ECG>EGCG >>EGC≈EC,which was related to the number of hydroxyl groups on catechin B-ring and the galloyl moiety structure on C-ring.The interactions between BSA and these catechin were static quenching mechanism,and the protein-ligand complexes were formed.The binding location of EGCG or ECG to BSA primarily took place in site I(i.e.subdomain IIA),whereas the binding of EC or EGC to BSA did not locate in site 1 nor site 2.2.Then,the interactions between bioactive compounds(EGCG,Heme)and plasma protein(i.e.BSA,Human Serum Albumin(HSA),Immunoglobulin G(IgG),Fibrinogen(FG))were investigated.The fluorescence spectrum,molecular docking technique and ultraviolet-visible absorption spectrum were applied.The results showed that the affinities of EGCG to these proteins were in the order of BSA>HSA>IgG>FG,and the affinities of Heme to these plasma proteins followed the order of HSA>BSA>IgG≈FG.These different affinities were mainly related to the hydrophobic structure of these proteins.The interactions between plasma proteins and EGCG or Heme were static quenching mechanism,and protein-ligand complexes were formed.The binding location of EGCG to HSA primarily took place in site I(i.e.subdomain IIA),whereas the binding of Heme to HSA did not locate in site 1 nor site 2.Protein could simultaneously bind EGCG and Heme to form HSA-diligand complex.The cytotoxicity of Heme in endothelial cells was decreased in the HSA-diligand complexes relative to those of heme or HSA-Heme complex,where the stability of bioactive EGCG during storage was improved in the HSA-diligand complex relative to that in free flavonoid.