| topoisomerase | <enzyme> That change the degree of supercoiling in DNA by cutting one or both strands. Type I topoisomerases cut only one strand of DNA, type I topoisomerase of E. Coli (omega protein) relaxes negatively supercoiled DNA and does not act on positively supercoiled DNA. Type II topoisomerases cut both strands of DNA, type II topoisomerase of E. Coli (DNA gyrase) increases the degree of negative supercoiling in DNA and requires ATP. It is inhibited by several antibiotics, including nalidixic acid and ovobiocin. (18 Nov 1997) |
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| DNA topoisomerase | <enzyme, molecular biology> An enzyme capable of altering the degree of supercoiling of double stranded DNA molecules. Various topoisomerases can increase or relax supercoiling, convert single stranded rings to intertwined double stranded rings, tie and untie knots in single stranded and duplex rings, catenate and decatenate duplex rings. Topoisomerase II of E. Coli = gyrase. (18 Nov 1997) |
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| DNA topoisomerase (ATP-hydrolysing) | <enzyme> An ATP-requiring enzyme which, in the presence of magnesium ions, introduces negative supertwists into closed and possibly linear duplex DNA. The enzyme is implicated in DNA replication and transcription. It causes the storage of mechanical strain energy in the superhelical turns of DNA at the expense of ATP hydrolysis. Chemical name: DNA topoisomerase (ATP-hydrolysing) Registry number: EC 5.99.1.3 (12 Dec 1998) |