Study on the binding behavior of bovine serum albumin with cephalosporin analogues by chemiluminescence method

The luminol-bovine serum albumin chemiluminescence system was proposed for the first time. It was found that the hydrophilic luminol bound to the hydrophilic domain at Trp¹³⁴ of BSA with accelerating the electrons transferring rate of excited 3-aminophthalate, which led to the enhancement CL intensity of luminol at 425 nm. The increment of chemiluminescence intensity was proportional to the concentrations of bovine serum albumin from 5.0 × 10⁻¹¹ to 1.0 × 10⁻⁸ mol L⁻¹ with the linear equation of ΔI = 7.47C_BSA + 4.89 (R² = 0.9950). Based on the remarkable quenching effect of cephalosporin on the luminol-bovine serum albumin chemiluminescence system, the interaction of bovine serum albumin-cephalosporin was studied by flow injection-chemiluminescence method. A valuable model for studying the interaction of bovine serum albumin-cephalosporin was constructed and the formula lg[(I₀ − I)/I] = lg K_D + n lg[D] was obtained. The binding parameters calculated by the model did agree very well with the results obtained by fluorescence quenching method. The major binding force of bovine serum albumin with cephalosporins was the hydrophobic effect. The binding ability of cephalosporin analogues to bovine serum albumin followed the pattern: cefoperazone, ceftriaxone and cefotaxime > cefuroxime and cefaclor > cefadroxil, cefradine and cefazolin, which was close to the order of their antibacterial ability. Using flow injection chemiluminescence method also obtained the stoichiometric ratio, the average of association constant K_P and dissociation degree α of luminol-bovine serum albumin were 1:1, 1.12 × 10⁷ L mol⁻¹ and 0.086, respectively.