title: The unwinding of circular DNA by intercalating agents as determined by gel electrophoresis.
abstract: The conventional counting of electrophoretically resolvable topoisomers is an attractive technique for determining the number of superhelical turns in a closed circular DNA molecule. The method can be extended in order to determine the unwinding produced by a drug, if its binding constants are known under similar environmental conditions. Ethidium bromide was found to unwind a DNA molecule derived from the plasmid pBR322 by 26.0 degrees in a magnesium-containing buffer. The method is convenient for investigating the possible effects of different environmental changes (such as ionic strength, ionic species, or temperature) on the unwinding angle produced by a particular drug. It can also give an early indication of multiple modes of binding.
mesh_terms: D000818:Animals; D002417:Cattle; D004247:DNA; D004270:DNA, Circular; D004996:Ethidium; D005914:Globins / Q000235:genetics; D007364:Intercalating Agents; D007700:Kinetics; D009690:Nucleic Acid Conformation; D010957:Plasmids; D013329:Structure-Activity Relationship; D013950:Thymus Gland
chemical_list: D004270:DNA, Circular; D007364:Intercalating Agents; D005914:Globins; D004247:DNA; D004996:Ethidium