Abstract: 【Objective】 The purpose of this experiment was to study the binding mechanism of salafloxacin (SFX) and bovine serum albumin (BSA). 【Method】 The fluorescence spectroscopy method was employed to investigate the fluorescence quenching effect of SFX on BSA,the interaction type,binding mode,and number of binding sites between SFX and BSA.Synchronous fluorescence spectroscopy was used to measure the effect of SFX on the endogenous fluorescence of BSA,the influence of SFX on the fluorescence intensity of tyrosine (Tyr) and tryptophan (Trp) in BSA was analyzed.The three-dimensional fluorescence spectroscopy was employed to analyze the three-dimensional fluorescence characteristics of SFX and BSA,and the effect of SFX on the conformation of BSA was analyzed.Ultraviolet-visible spectroscopy was employed to detect the UV spectral characteristics of BSA upon addition of varying concentrations of SFX，the effect of SFX on the conformation of BSA and the type of quenching was analyzed.The binding sites and binding forces between SFX and BSA were analyzed by molecular docking method，and the effect of metal ions on the binding of SFX and BSA was analyzed by fluorescence spectroscopy. 【Result】 Fluorescence spectroscopy detection results showed that SFX quenched the endogenous fluorescence of BSA,and the quenching type of BSA was static quenching.The binding process between SFX and BSA was exothermic and spontaneous，non radiative energy transfer occurred during the binding process.The interaction between SFX and BSA was primarily mediated by hydrogen bonding and van der Waals forces.The number of binding sites was approximately 1.The molecular binding distance was 3.182 nm.Synchronous fluorescence detection showed that SFX quenched the fluorescence of Tyr and Trp residues as well as the peptide backbone in BSA.Three-dimensional fluorescence spectroscopy demonstrated a decrease in fluorescence intensity of Trp and Tyr residues induced by SFX,and the peptide chain structure of BSA was alterated.Molecular docking showed that SFX formed hydrogen bonds with Pro498,Glu470 and Lys533 residues in BSA,hydrophobic bonds with Val497 and Lys499 residues,and van der Waals forces with Tyr496 residue.The metal ions Ca²⁺,Na⁺,K⁺ and Al³⁺exhibited a promoting effect on the binding of SFX to BSA，Fe²⁺,Mg²⁺ and Cu²⁺ exhibited inhibitory effects. 【Conclusion】 SFX-BSA binding was spontaneous,forming a stable complex,and the combination would change the conformation of BSA.This study provided fundamental data for investigating SFX toxicity,in vivo transport and metabolic mechanisms.

Key words: bovine serum albumin (BSA); salafloxacin (SFX); spectral method; molecular docking; metal ion