Figure 7.

Competition between ciprofloxacin and the quinazolinedione to induce plasmid DNA cleavage by GyrA^S83L/D87N gyrase. An amount of 50 µM quinazolinedione (the concentration at which maximal cleavage was achieved with this drug–enzyme combination) was included simultaneously in all reactions with 0–500 µM ciprofloxacin to determine the ability of the quinolone to compete with the quinazolinedione for interaction with the enzyme. The level of cleavage seen in the presence of the quinazolinedione alone was set to 100%. Error bars represent the standard deviation of three independent experiments.