Spectroscopic Study On The Interactions Of BSA With Three Drugs

The interactions between drugs and proteins are important for chemistry biology investigation. Serum albumin, the most abundant protein in blood plasma, can bind a great variety of exogenous and endogenous compounds extensively. Investigation on the binding mechanism of drugs with serum albumin is much important in pharmacokineties and toxicology. Thus, it became an interesting research field of life seiences, chemistry and clinieal medieine. Bovine serum albumin is similar with Human serum albumin but more cheaper. In this dissertation, BSA as the model protein, researched the interactions between three drugs and BSA on the basis of the previous researeh. The contents of this thesis are divided into four chapters and are listed as follow:Chapter one, the structures, functions and natures of proteins were introduced briefly in bioanalytical chemistry. Then the interactions of different kinds of small ligands with serum albumin were reviewed in turns. The methods, contents, the current situation are summarized. Under predicting the development of the binding of BSA and drugs, the conception of this thesis are put forward.Chapter two, the interaction between 5-hydroxycamptothecin (5-HCPT) and bovine serum albumin (BSA) was investigated using fluorescence and circular dichroism (CD) in aqueous solution at physiological conditions. After analyzing the fluorescence quenching data, we found that BSA had reacted with 5-HCPT and formed a certain new compound. The binding constants Kb and binding sites n were measured at different temperatures: 1.867×10⁵L·mol^-1 and 1.220 at 298K, 1.850×10⁵L·mol^-1 and 1.211 at 304K, 1.829×10⁵L·mol^-1 and 1.217 at 310K. Thermodynamic parameters such as ?G, ?H and ?S, were calculated at different temperatures, showing that hydrophobic interaction was mostly responsible for the binding of 5-HCPT to BSA. Furthermore, site marker competitive displacement experiments demonstrated that 5-HCPT binds with high affinity to site I (subdomain IIA) of BSA. At last, synchronous fluorescence and CD spectra showed that the conformation of BSA before and after interacting with 5-HCPT has been changed. Chapter three, the interaction between caffeic acid (CaA) and bovine serum albumin (BSA) was investigated using fluorescence and circular dichroism (CD) in aqueous solution at physiological conditions. The results revealed that CaA can quench the BSA fluorescence with a static mode, indicating that caffeic acid reacts with BSA. The binding constants and number of binding sites at 298K were estimated as 8.118×10³mol/L and 1.249, which indicated that hydrophobic interaction was the dominant intermolecular force. Site marker competitive experiments indicated that the binding of CaA to BSA primarily takes place in subdomain IIA of BSA. Synchronous fluorescence and CD spectra showed that the conformation of BSA before and after interacting with CaA has been changed. Furthermore, the effects of metal ions on CaA-BSA association was elucidated.Chapter four, the interaction of Cu²⁺-Qct complex with BSA was studied by fluorescence spectroscopy, CD, and supplied by UV-vis absorption spectroscopy in Tris buffer. The binding parameters of Cu²⁺-Qct complex to BAS were investigated as well. The probable fluorescence quenching of BSA by Cu²⁺-Qct complex is a static procedure; electrostatic interaction played a major role in stabilizing the BSA-(Cu²⁺-Qct complex) system. The results also demonstrated that Cu²⁺ can affect the interaction of Qct with BSA to a considerable degree. Synchronous fluorescence spectroscopy and CD indicated that the conformation of BSA molecule is changed with addition of Cu²⁺-Qct complex. In addition, the binding site of Cu²⁺-Qct complex is located in the hydrophobic pocket of subdomain IIA of BSA.