Binding characteristics of aflatoxin B₁ with free DNA in vitro

In this paper, the binding characteristics of aflatoxin B₁ (AFB₁) with the herring sperm deoxyribonucleic acid (DNA) in vitro were investigated through different analytical methods. The ultraviolet-visible spectroscopy (UV-vis), fluorescence, and circular dichroism (CD) spectra results showed that a new AFB₁-DNA complex was formed. All the results suggested that AFB₁ interacted with free DNA in vitro in an intercalating binding mode. The results of the DNA melting experiments also showed that the melting temperature of DNA increased by about 12.1 °C due to the addition of AFB₁, which was supposed to be closely related to the intercalation of AFB₁ into DNA. The agar gel electrophoresis experiments further confirmed that the binding mode of AFB₁ and free DNA in vitro was indeed intercalation. In addition, the fluorescence quenching induced by adding AFB₁ to the ethidium bromide-DNA (EB-DNA) mixture indicated the presence of competitive non-covalent intercalating binding interaction with a competitive binding constant of 5.58 L/mol between AFB₁, EB, and DNA. The thermodynamic data demonstrated that the main driving forces of the binding reaction were van der Waals forces and hydrogen bond. The resonance light scattering (RLS) assay results showed that the DNA binding saturation values of AFB₁, EB, psoralen (PSO), and angelicin (ANG) were 2.14, 15.59, 0.74, and 0.74, respectively. These results indicated that the DNA binding capacity of AFB₁ was weaker than that of EB, but stronger than those of PSO and ANG.