DNA topoisomerase I from Alcaligenes eutrophus H16.

Molecular and functional properties of DNA topoisomerase I isolated from a hydrogen-oxidizing bacterium, Alcaligenes eutrophus H16, were investigated. Under native conditions the enzyme forms a monomer with a relative molar mass of 98,500. A rod-like shape of the molecule was derived from the calculated frictional coefficient. The isoelectric point of the enzyme was determined to be in the range of 7.6-8.0. The enzyme activity is strictly Mg2+ dependent with an optimum at 3 mM Mg2+. The pH optimum ranges within 7.5-9.0. A. eutrophus DNA topoisomerase I activity is inhibited by M13 ssDNA, high ionic strength, polyamines, heparin and by a number of intercalating drugs.