INTERACTIONS BETWEEN FLUOROQUINOLONES, MG2-PHASE SYSTEM AND BY AFFINITY-CHROMATOGRAPHY(, DNA AND DNA GYRASE, STUDIED BY PHASE PARTITIONING IN AN AQUEOUS 2)

The primary target of fluroquinolones has been identified as the enzym e DNA gyrase, but the mechanism of action of these antibacterial agent s is still a matter of controversy. Using partitioning in aqueous poly ethylene glycol (PEG)-dextran systems, the affinities of several fluor oquinolones for DNA were determined with accuracy and at equilibrium. It was proved that the binding was strongly dependent on the ability o f the drugs to bind Mg2+ with K-A values of about 40 000 l mol(-1), bu t was poorly related to the antibacterial activity [minimal inhibitory concentration (MIC) and gyrase inhibition]. Using affinity chromatogr aphy on immobilized fluoroquinolone, it was shown that DNA gyrase was unable to bind fluoroquinolones in the absence of DNA, but that a DNA- quinolone-gyrase complex was formed in the presence of Mg2+.