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en.wikipedia.org/wiki/Topoisomerase

Discovery. In the 1970s, James C. Wang was the first to discover a topoisomerase when he identified E. coli topoisomerase I. Topo EC-codes are as follows: type I, EC 5.99.1.2; type II: EC 5.99.1.3. Function. The double-helical configuration of DNA strands makes them difficult to separate, which is required by helicase enzymes if other enzymes are to transcribe the sequences that encode ...

en.wikipedia.org/wiki/Type_I_topoisomerase

The human topoisomerase type IB enzyme forms a covalent 3'-phosphotyrosine intermediate, the topoisomerase 1-cleavage-complex (Top1cc). The active irinotecan metabolite, SN-38, acts by trapping (making a ternary complex with) a subset of Top1cc, those with a guanine +1 in the DNA sequence.

answers.yahoo.com/question/index?qid=20090225015058AAp6nzs

What is the difference between type one and two topoisomerase? ... Type I topoisomerase cuts one strand of a DNA double helix and then reanneals the cut strand. Type I topoisomerases are subdivided into two subclasses: type IA topoisomerases which share many structural and mechanistic features with the type II topoisomerases, and type IB ...

www.medicinenet.com/script/main/art.asp?articlekey=32631

Topoisomerase: A class of enzymes that alter the supercoiling of double-stranded DNA. (In supercoiling the DNA molecule coils up like a telephone cord, which shortens the molecule.) The topoisomerases act by transiently cutting one or both strands of the DNA.

www.ebi.ac.uk/interpro/potm/2006_1/Page2.htm

Topoisomerase I inhibitors induce single-strand breaks into DNA, and can work by a variety of mechanisms. Some drugs, such as camptothecins, inhibit the dissociation of topoisomerase and DNA, leading to replication-mediated DNA damage, which can be repaired more efficiently in normal cells than in cancer cells (deficient for DNA repair).

www.ebi.ac.uk/interpro/potm/2006_1/Page1.htm

DNA Topoisomerase By Jennifer McDowall The DNA in the nucleus of a cell contains all the information it requires to carry out life’s processes: growth, development, maintenance, reproduction and protection. With all this information, it is no wonder that the length of a cell’s DNA is far greater than that of the cell compartment that contains it - the DNA in a single human diploid cell ...

www.selleckchem.com/Topoisomerase.html

Nalidixic acid is a synthetic 1,8-naphthyridine antimicrobial agent with a limited bacteriocidal spectrum. It is an inhibitor of the A subunit of bacterial DNA gyrase. S7261: Beta-Lapachone. Beta-Lapachone is a selective DNA topoisomerase I inhibitor, exhibiting no inhibitory activities against DNA topoisomerase II or ligase. Phase 2. S4006 ...

www.ncbi.nlm.nih.gov/pmc/articles/PMC2748742

Box 1. Many different classes of compounds target Topoisomerase II. Drugs targeting topoisomerase II fall into two categories, Top2 poisons and Top2 catalytic inhibitors. Many Top2 poisons have demonstrated anti-cancer activity. Top2 poisons can be further sub-divided into intercalating and non-intercalating poisons.