he First HospitalSubunit A and B proteins of DNA gyrase from Klibsiella pneumoniae 900129 were successfullyand seperately purified by the combined method of bacterial lysis using lysozyme

protein pro-cipitation with ammonium sulfate and affinity chromatography on novobiocin Sephero-se CL-6B

Both uncoupled subunit A and B had no enzymatic activities.But the reconstituted holoen-zyme with subunit A and B counld c0nverse the relaxed plasmid pBR322 into supercoiling form。Quinolone could inhibit the supercoiling activity of DNA gyrase。 The 50% inhibitory concentra-tion(IC50)of nalidixic acid

norfloxacin

ofloxacin

sparfloxacin and ciprofloxacin were 10. 46、1. 35、0.35、0.42、0.12μg/ml respectively. The IC50 of quinolone were correlated with their MICs。