Canadian Medical Guide > Chemicals and Drugs > Enzymes and Coenzymes > Enzymes > Isomerases > DNA Topoisomerases Terms and Definitions

DNA Topoisomerases

Medical Definition:	Enzymes that regulate the topology of DNA by actions such as breaking, relaxing, passing, and rejoining strands of DNA in cells. These enzymes are important components of the DNA replication system. They are classified by their substrate specificities. DNA TOPOISOMERASE, TYPE I enzymes act on a single strand of DNA. DNA TOPOISOMERASE, TYPE II enzymes act on double strands of DNA.
CAS Number:	EC 5.99.1.-
Previously Indexed:	DNA Topoisomerase (1977-2001),DNA Topoisomerase (ATP-Hydrolysing) (1979-2001)

DNA Topoisomerases Categories.

	DNA Topoisomerases, Type I - DNA TOPOISOMERASES that catalyze ATP-independent breakage of one of the two strands of DNA, passage of the unbroken strand through the break, and rejoining of the broken strand. DNA Topoisomerases, Type I enzymes reduce the topological stress in the DNA structure by relaxing the superhelical turns and knotted rings in the DNA helix.
	DNA Topoisomerases, Type II - DNA TOPOISOMERASES that catalyze ATP-dependent breakage of both strands of DNA, passage of the unbroken strands through the breaks, and rejoining of the broken strands. These enzymes bring about relaxation of the supercoiled DNA and resolution of a knotted circular DNA duplex.

DNA Topoisomerases Medical Definitions and Terms

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