Influence of metal ions on the interaction between gatifloxacin and calf thymus DNA

To study the interaction between gatifloxacin (GT), metal ions (Cu2+, Cd2+, Co2+, Mg2+) and calf thymus DNA under condition of physiology pH, UV absorption and fluorescence methods were adopted. Result shows that metal ions and DNA are able to react with GT in ground state. In further research, by studying the influence of metal ions on binding of GT with DNA in metal ions–GT–DNA ternary system, we found that influential mechanism of Mg2+ on the binding of GT with DNA may be different from the other three. Mg2+ can act as a bridge in the binding of GT's carboxyl/carbonyl with DNA phosphate in certain concentration range; while Cu2+, Cd2+, Co2+ can combine directly with GT by reaction between GT carboxyl/carbonyl and DNA base, and enhance the binding ability of GT with DNA. The influence extent and type depend not only on the binding site of DNA with metal ions (phosphate or base), but also the binding ability of which. The stronger the binding ability of metal ions with DNA base is, the larger their promotion to binding of GT with DNA is. The order of metal ions’ influential ability on the binding of GT–DNA is identical to the binding ability order of metal ions with DNA base, that is: Cu2+ > Cd2+ > Co2+ > Mg2+.