Spectroscopic Studies Interactions Between Seven Drugs And Proteins

Serum albumin and pepsin have important physiological functions in vivo.Serum albumin can carry,transport and metabolize a variety of compounds.Investigation of the interactions between serum albumin and natural small molecule drugs will be of great of help to understand the mechanism of drug transportation in body,helping people to understand the metabolism of drugs in the body.Pepsin can digest a variety of substances in the body.When a drug is taken into body,it must interact with pepsin initially.The study of interactions of pepsin and small molecules will be helpful for the understanding of drug distribution and drug delivery optimization.The results of this thesis can be of clinical,pharmacokinetics use and will do the development of new drugs a great favor.In this thesis,interactions between several small natural drugs and serum albumin or pepsin are investigated by the method of fluorescence spectroscopy and molecular docking,including:?1?The fluorescent quenching of evodiamine and rutaecarpine to both bovine serum albumin and human serum albumin were carried out under simulated physiological conditions of water bath temperature 37 ? and p H 7.4.The experimental data are analyzed by Stern-Volmer equation and double logarithmic equation.The mechanism of quenching is deduced as static quenching with the host-guest molar ratio 1: 1.The binding constants are as follows: K_A,BSA-Evo = 1.02 × 10³,K_A,HSA-Evo = 5.75 × 10³,K_A,BSA-Rut = 8.5 × 10⁴,K_A,HSA-Rut = 1.2 × 105.Synchronous fluorescence results show that the binding between host and guest can change the micro-environment and configuration of the host.Molecular docking results indicate that both evodiamine and rutaecarpine can be adopted by a hydrophobic pocket of the two serum albumins which locate close to a Trp residue.?2?The interaction between cytisine and pepsin was studied under simulated physiological conditions of water bath temperature 37 ? and p H 2.Fluorescence results show that the fluorescent emission of pepsin can be quenched by the addition of cytisine.The quenching mechanism is calculated as static quenching.The binding site numbers and the apparent binding constant are calculated from fluorescent data measured at different temperatures.Thermodynamic parameters such as ?H,?S and ?G are calculated either which indicate the Van der waals' forces and hydrogen bonds play important roles to the formation of the complex.Synchronous fluorescent research shows the adoption of cytisine can change micro-environment of a Trpresidue and induce the configuration of the host as well.Additionally,molecular docking results showed that the guest is embraced into a hydrophobic pocket by pepsin and there exists hydrogen bonding between pepsin and cytisine.?3?The interaction between fisetin and pepsin was studied under simulated physiological conditions of 37 ? water bath and p H 2.Fluorescence results show that the fluorescent emission of pepsin can be quenched by the addition of fisetin.The quenching mechanism is inferred as static quenching.The binding site numbers and the apparent binding constant are calculated from fluorescent data measured at different temperatures.Thermodynamic parameters such as ?H,?S and ?G are calculated either which indicate the Van der waals' forces and hydrogen bonds play important roles to the formation of the complex.Synchronous fluorescent research shows the adoption of fisetin can change micro-environment of some AA residues and induce the configuration of the host as well.Additionally,molecular docking results showed that the guest is embraced into a hydrophobic pocket,formed by Tyr75,Met290 etc.,by pepsin and there exist hydrogen bonding between cytisine and Asp215,Tyr189 and Ile128.?4?Toinvestigate the interactions between flavonoid glycosides and protein,three flavonoid compounds including naringenin,naringin and naringin dihydrochalcone are chosen as guest molecules.Simulated physiological conditions of 37 ? water bath and p H 2 are fixed as environmental parameters.Fluorescence results show that the fluorescent emission of pepsin can be quenched by the addition of all three naringenin flavonoids.The quenching mechanisms are inferred as static quenching.The binding site numbers and the apparent binding constant are calculated from fluorescent data measured at different temperatures.At 37 ?,the apparent binding constants of naringenin,naringin and naringin dihydrochalcone to pepsin are 0.39 × 10⁴,0.45 × 10⁴,and 0.78 × 10⁴.Thermodynamic parameters such as ?H,?S and ?G are calculated either which indicate the Van der waals' forces and hydrogen bonds play important roles to the formation of the complexes.Synchronous fluorescent research shows the adoption of guests can change micro-environment of some AA residues and induce the configuration of the host as well.Additionally,molecular docking results showed that pepsin will form a hydrophobic pocket to include guests.Due to the molecular sizes,naringenin and naringin can be hosted into the pocket but naringin dihydrochalcone locates at the surface of the host.