| The interaction between serum albumin and bio-active drugs has attracted great interest among researchers since several decades ago.The drug-protein interaction has important effect on the distribution,free concentration and the metabolism of drugs in the blood stream.Therefore, studies on the binding of drug with protein will facilitate interpretation of the metabolism and transport process of drug,and will help to explain the relationship between structures and functions of proteins.The work in this thesis mainly concerns about the interaction between several Chinese herbal bio-acvtive components and bovine serum albumin(BSA). Trans-resveratrol and the flavonoids were selected to study the structure-affinity relationship,and the effect of metal ion on the interaction between Chinese herb bio-acvtive components and BSA.The studies were performed on three ports as such follow:(1) The interaction of trans-resveratrol and BSA was investigated by means of fluorescence quenching,resonance light scattering,ultraviolet spectroscopy and Fourier transform infrared spectroscopy.The intermolecular action signals of the trans-resveratrol-BSA systems were studied and idiographic information of trans-resveratrol-BSA interaction were obtained from above signals,thereout,the relatively consummate information system of Chinese herbal active component-BSA interaction was constructed.Binding of trans-resveratrol to BSA quenches the BSA fluorescence and static quenching occur with complex formation.The apparent binding constants between Trans-resveratrol and BSA were 1.95×106(293.15 K),1.70×106(303.15 K) and 1.65×106 L·mol-1(313.15 K), and the binding distances(r) between Trans-resveratrol and BSA were calculated.The negative entropy change and enthalpy change indicated that the interaction of Trans-resveratrol and BSA was driven mainly by electrostatic forces.The process of binding was a spontaneous process in which Gibbs free energy change was negative.The interaction of Trans-resveratrol and BSA was confirmed by synchronous fluorescence and FT-IR spectra. (2) Two flavonoid aglycones(daidzein and genistein) and their glycosides(daidzin and genistin) are studied for their affinities for BSA. The effect of glycosylation of flavonids on binding with serum albumin was discussed.The apparent binding constants between daidzein,daidzin, genistein,genistin and BSA were 2.72×105,1.91×104,1.22×106 and 3.35×104 L·mol-1,respectively.The results indicates that the glycosylation of flavonoids affects the binding process;in general,the glycosylation decreases the binding affinity.Glycosidation could lower the affinity for BSA by one to two orders of magnitude depending on the conjugation site.This result partly supports that the flavonoid aglycones are easier absorbed than flavonoid glycosides.(3) The effect of Zn2+ on the interaction between four differently substituted B-ring hydroxylation flavonols(galangin,kaempferol, quercetin,myricetin) and BSA was investigated by means of fluorescence spectroscopy.The binding constants between galangin,kaempferol, quercetin,myricetin and BSA were 1.08×106,5.08×106,3.70×107, 2.15×108 L·mol-1,respectively.When Zn2+ was added,the binding constants changed to 3.09×105,2.18×105,1.3×105,7.40×104 L·mol-1, respectively.The results show that the binding constants and the number of binding sites decreased after the addition of Zn2+ to BSA and flavonols. The binding affinity decreased more with the increasing number of-OH moieties on the B-ring of flavonol with the addition of Zn2+.(4) In order to rescerch the reaction mechanism,the effect of Zn2+ on the interactions between quercetin,myricetin and BSA was investigated by means of fluorescence spectroscopy,ultraviolet spectroscopy and Fourier transform infrared spectroscopy.Taken the results together,it can be concluded that the effect of Zn2+ on the interactions of quercetin, myricetin with BSA in aqueous solution may be ascribed to the formed zinc complex. |
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