DNA gyrase from Streptomyces noursei and comparison with gyrases from other sources: Gyr B subunit may affect the pH‐dependence of the enzymic activity

Purified subunits of DNA gyrase from Streptomyces noursei have been obtained with relatively high yield. By comparing the activity of the reconstituted enzyme (supercoiling and cleavage reaction) with other gyrase species and hybrid enzymes it is shown that the reactivity of gyrases in vitro may differ significantly with pH, an effect not previously reported. The pH-effects on gyrase and hybrid enzyme activity seems to be largely determined by the Gyr B protein.