FIG. 5.

Quinolone binding to the gyrase-DNA complex. Spin column chromatography data from a number of experiments show the binding of ciprofloxacin (CFX) to WT and mutant (Ala⁸³ Ala⁸⁷) gyrase-DNA complexes. Reaction mixtures containing [³H]-CFX were passed through Sephadex spin columns, and the amount of drug bound was estimated by scintillation counting. The enzyme concentration was 130 nM in terms of the GyrA monomer. Data were fitted to simple 1:1 ligand binding curves and yielded the following K_d^app values: 7.3 ± 3.1 μM for the WT (○) and 78.0 ± 35.6 μM for the mutant (●).