Abstract：The interaction between pharmaceutical and protein is an important pharmacokinetic characteristic. Most kinds of drugs must reach the receptor to perform the pharmacological function by plasma. Albumins can serve as a depot protein and a transport protein for numerous endogenous and exogenous compounds. It is of great significance to investigate the binding interaction between albumin and drugs, since it can not only help understand the transportation and distribution of drugs but also elucidate the mechanism. Under the physiological condition of body, the interaction between levofloxacin (LVFX) and bovine serum albumin (BAS) was investigated by fluorescence spectra and ultraviolet absorbance (UV) spectra based on liquid drop. The experimental results showed that LVFX quenches the fluorescence of BAS by forming a LVFX-BSA complex. According to Lineweaver-Burk equation, the apparent binding constants (KLB) between LVFX and BSA were 1.694 9×105 L·mol-1 (291 K) and 2.881 0×105 L·mol-1 (310 K), and the binding sites (n) were 0.884 9 (291 K) and 0.808 9 (310 K). Thermodynamic parameters could be evaluated from the thermodynamic second law, with ΔΗ (enthalpy) being 20.94 kJ·mol-1 and ΔS (entropy) being 172.1 J·mol-1. According to the relation between thermodynamic parameters and the interaction force, LVFX depended principally on the hydrophobic interaction to bind with BSA. The results showed that the quenching belonged to static fluorescence quenching with non-radiation energy transfer happening within single molecule. The binding locality was an area 2.68 nm away from tryptonphan residue-212 in BAS according to Frster’s non-radiation energy transfer mechanism. The conformational changes of BSA were evaluated by measuring the synchronous fluorescence intensity of protein amino acid residues, both before and after the addition of LVFX. A slightly stronger blue-shift of tryptophan fluorescence upon the addition of drug was observed, and the emission maximum of tyrosine kept its position. It was suggested that the environments of tryptophan residues in pure albumin solution are relatively polar. Binding of LVFX changes the environments to apolar ones. The shift in polarity is brought about by confirmation changes due to the interaction between albumin and ligand molecule.
Key words：LVFX;BSA;Fluorescence of liquidrop;Binding reaction;Thermodynamic parameters
陈泽忠,冯锋*,杨文娟,梁文娟,李仁军,王诚. 左氧氟沙星与牛血清白蛋白相互作用的液滴荧光法研究[J]. 光谱学与光谱分析, 2008, 28(07): 1612-1616.
CHEN Ze-zhong, FENG Feng*,YANG Wen-juan,LIANG Wen-juan,LI Ren-jun,WANG Cheng. Investigation of Interaction between Levofloxacin and Bovine Serum Albumin by Fluorescence Analysis Based on Liquid Drop. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2008, 28(07): 1612-1616.
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