Study Of The Interaction Between Quinolones And Bio-macromolecules

Protein and DNA are important bio-macromolecules in the life;they have respective biological function and have been playing many vital roles for all kinds of biological phenomena. Exploring the interaction mechanisms on these bio-macromolecules with small molecules or ions, especially for those targeting-drug molecules, at the molecular level is of current interest in many research areas such as biology, clinical medicine, medicinal chemistry, chemistry and so on. Quinolone drug is a kind of antibacterial drugs which have been used widely in clinical medicine, but its pharmacology and toxicology still have to be studied further. There are many metal ions in the organism, and they participate in many important vital action. Metal ions can compound with quinolone drug, and also can combine with bio-macromolecules such as protein. This paper studied the interaction mechanisms among quinolone drug, metal ions and bio-macromolecules, and it was consisted of three parts.In the first part, calf thymus DNA, transitional metal ions (Fe³⁺ and Cu²⁺) and quinolone drugs (pazufloxacin and balofloxacin) have been selected for investigative object, and the binding characteristics and mechanism of quinolone antibiotics to DNA have been investigated by using the methods of fluorescence spectroscopy, absorbance spectroscopy and viscosity. The spectroscopy analysis shows that metal ions (Fe³⁺ and Cu²⁺) and DNA both can quench the endogenous fluorescence of the two kinds of quinolone drugs, and the fluorescence intensity of quinolone drugs quenched by calf thymus DNA was aggravated in the presence of metal ions. Based on the change of fluorescence intensity and fluorescence quench formulas, the quenching constants and resultant constants between metal ions and quinolone drugs have been worked out, and the results show that the fluorescence quenching effect of metal ions on quinolone is because of a static energy transfer mechanism, and the number of binding sites between metal ions and quinolone were deduced to be 1. The experimental results of viscosity show that the binding mode of quinolone (pazufloxacin and balofloxacin) with DNA is groove binding.In the second part, transitional metal ions (Fe³⁺ and Cu²⁺), bovine serum albumin (BSA) and quinolone drugs (pazufloxacin and balofloxacin) have been selected forinvestigative object, and the binding characteristics and mechanism of quinolone antibiotics to BSA have been investigated by using fluorescence spectroscopy and absorbance spectra. The two quinolone drugs both can quench the endogenous fluorescence of BSA regularly and the quenching was not initiated by dynamic collision but from compound formation, it was a static quenching process. Based on the experimental results, the equilibrium constants and the number of binding sites for the two quinolone drugs in this research interacting with BSA are measured, the transfer efficiency of energy and distance between these drugs and BSA are obtained in view of the theory of Forster energy transfer. The interaction between the two quinolone drugs and BSA in the presence of metal ions was also studied. The interaction between BSA and pazufloxacin can be promoted by Cu2+ ion, but decreased by Fe3+ ion. And the interaction between BSA and balofloxacin can be increased by metal ions (Fe3+ and Cu2+).In the third part, Cu2+ ion, gatifloxacin and C-phycocyanin (C-PC) have been selected for investigative object, and the interaction between gatifloxacin and C-PC in the presence of Cu2+ ion has been studied by the means of fluorescence spectra and UV absorbance spectra. The experimental results show that there is a stable complex formed between Cu2+ ion and gatifloxacin, and an unstable complex formed between Cu2+ ion between C-PC. The results also show that the interaction between gatifloxacin and C-PC is weak, but it can be improved by the presence of Cu2+ ion, this means that there must be a ternary complex formed among Cu2+ ion, gatifloxacin and C-PC, and Cu2+ ion plays a stimulative role as a bridge in the interaction between gatifloxacin and C-PC.