| Serum albumin,which is the most abundant protein of blood plasma,plays key physiological roles in the balance of osmotic blood pressure and is essential for transportation,distribution and metabolism of many endogenous and exogenous ligands.Drug molecules in the general circulation are either bound reversibly to plasma proteins or exist in unbound(free)form.Only free drug molecules have the pharmacological activity.Therefore,the investigation of binding interaction of drug molecules with serum albumin has great significance in discovering pharmacokinetic and pharmacodynamics implications,which is an essential step for a new drug design.Apart from that,the interaction experiment is helpful for revealing the transportation and distribution of the drugs in vivo,explaining the toxicity at the molecular level.The interaction between cytosine nucleoside analogues FNC/cytidine(CDPC)/5’-cytidine acid(5’-CMP),oyrazolidinones aminopyrine(AMP)/antipyrine(ATP)/4-aminoantipyrine(AAP),methyl yellow purine derivatives theophylline(Tph)/ doxofylline(Dfy),3-methoxy-1,2-naphthoquinone analogues and bovine serum albumin(BSA)under physiological conditions was investigated using fluorescence,UV absorption spectroscopy and molecular modeling methods.According to fluorescence spectra,the results indicated that FNC/CDPC/5’-C MP,AMP/ATP/AAP,Tph/Dfy and 3-methoxy-1,2-naphthoquinone analogues cou ld quench the intrinsic fluorescence of BSA and the quenching mechanism wer e static quenching.Then the binding constant and binding sites number at diff erent temperatures were measured according to double-logarithm regression equ ation.The thermodynamic parameters obtained from the Van’t Hoff equation an d molecular modeling study results showed that the binding site for FNC/CDP C/5’-CMP was in the subdomain IIA and IIB of BSA combined with hydropho bic interaction;For AMP,it was in subdomain II of BSA and the main intera ction forces was Van der Waals and hydrogen bonding interactions,meanwhile the hydrophobic interaction also existed;For ATP,it was in subdomain II of BSA and the main interaction forces was hydrophobic interaction;For AAP,itwas in subdomain II of BSA and the main interaction forces was hydrophobi c and electrostatic interaction;For Tph/Dfy,they were in subdomain IIIA of B SA and the main interaction forces was Van der Waals and hydrogen bonding interactions,meanwhile the hydrophobic interaction also existed;For 3-methoxy-1,2-naphthoquinone analogues,the main interaction forces were hydrophobic in teraction for analogues c,d,f,g and h,while for analogues a,b and e,the main interaction forces were hydrophobic and electrostatic interaction.The dista nce,r between the donor(BSA)and acceptor(the ligands)was calculated base d on the F?rster’s theory of non-radiation energy transfer and was found 2nm<r<7nm,which indicated that the energy transfer from BSA to these ligands occ urred with high probability.Additionally,as shown by synchronous fluorescenc e and three-dimensional fluorescence results,these ligands could lead to confor mational and some microenvironmental changes of BSA. |
