Study On The Interaction Between Active Ingredients Of Chinese Medicine Danshen And Serum Albumin

Study on drug-protein interaction is an indispensable content in the research anddevelopment of new drugs. On the one hand, it has directly effects on thepharmacokinetic behavior of the drug, including absorption, distribution, metabolismand excretion. On the other hand, it is of great theoretical significance to clarify thebasic issues, such as the relationship between protein structure and function, thebinding between enzyme and inhibitor and description of protein structuralcharacteristic and so on. Therefore, the research of the interaction between activeingredients of Chinese medicine and protein has become an important research topicin the field of life science, clinical medicine and medicinal chemistry and so forth.Spectroscopic methods are employed to investigate the interactions between activeingredient of Danshen (salvianolic acid B (SAB) or rosmarinic acid (RA)) and serumalbumins, the relationship between structure and affinity, and the effect of thirdsubstance on the binding in this thesis. The main conclusions are shown as follow:1. The study of interaction in many aspects: The interaction between SAB/RA andserum albumins were studied by means of multi-spectroscopic methods. Theexperimental results showed that the fluorescence of serum albumins was quenchedby drug through a combined quenching (static and dynamic) procedure, but the staticquenching was the dominant one. The binding affinity of SAB with serum albuminswas greater than that of RA. The binding reaction was spontaneous, and thehydrophobic interactions played a major role in binding of drug to protein. Serumalbumins had a single class of binding site at Sudlow’ site I in subdomain IIA for drug.Based on the F rster theory of the non-radiation resonance energy transfer, thenon-radiation energy from proteins to drugs occurred with high possibility and thebinding distances between drugs and proteins were all less than8nm. Moreover, thebinding of drug to serum albumins induced the alterations of secondary structure andtertiary structure of protein.2. The effect of metal ions on the binding: The effects of Cu2+and Fe3+on theinteraction between SAB/RA and serum albumins were investigated by fluorescencespectra. The quenching mechanism for SAB/RA to serum albumins was based on thestatic quenching (mainly) combined with dynamic one irrespective of the absence or presence of metal ions. The conformational change of serum albumins caused by thepresence of metal ions may be the main reason for the change of binding constant andbinding mechanism.3. The effect of catechins on the binding: To explore structure-affinity relationship,catechins (EC, EGC, ECG, EGCG) were selected to investigate the binding processwith BSA by using fluorescence spectroscopic method. The fluorescence datarevealed the strongest binding affinity to BSA was found for ECG (with the galloylmoiety on the C-ring and the catechol group on the B-ring). The presence ofcatechins did not change the quenching mechanism of drug with BSA, and all of thefluorescence quenching was mainly initiated by a static quenching procedure, but cannot ignore the dynamic one. The changes of interaction mechanism between drugs andBSA in the presence of catechins were because of the conformational change of BSAinduced by catechins and the formation of catechin-drug complex.4. The effect of Au nanoparticles (AuNPs) on the binding: Three different sizes ofAuNPs (14.31nm,16.51nm and31.76nm) were obtained and characterized. All thefluorescence quenching mechanism between drugs and BSA was a combinedquenching (static quenching, the main mode) regardless of the absence or presence ofAuNPs. The conformational change of BSA induced by the presence of AuNPs maybe the main reason for the change of binding mechanism.