The DNA Gyrase;gyrase is also called the cyclotron enzyme, the invertase, the rotation enzyme. belongs to one of the unwinding enzymes class, which is a topological isomerase II (Type II Topoisomerase;topo II), which is first found
in Escherichia coli. Consisting of two alpha subunits and two β subunits respectively, the molecular weight of 4x10^5 (wherein α subunit molecular weight about 1.05x105,β subunit molecular weight of about 9.5x104). It is the function of hydrolysis of ATP at the same time can make the relaxation of cyclic DNA into negative ultra-helical DNA. This role is complex and involves three steps: (1) First the DNA cyclotron enzyme binds with DNA to distort the cyclic DNA and form a "right-hand knot" structure, in which a stable positive helix is formed, and a negative super-helix is introduced, and (2) the enzyme then interrupts the double-stranded DNA behind the right-hand knot, And put it on the front of another double chain, so that the right-handed positive spiral into a left-handed negative super-helix; (3) Finally, the breakpoint is connected together. The introduction of the DNA negative hyper-helix can reduce the energy required to interrupt the base pair by about 4.1kJ Mol-1, which facilitates separating the DNA from the double strand. During the copy process, when a new strand of DNA is formed on the template, the DNA cyclotron transforms the DNA double strand into a natural, negative, super-helical configuration that requires ATP hydrolysis to provide energy. If ATP is absent, the enzyme catalyzes negative hyper-helix relaxation.
DNA cyclotron Enzymes
