From Big Medical Encyclopedia

DEOXYRIBONUCLEASES (dezoksiribonukleinat — an oligonukleotidogidrolaza and dezoksiribonukleinat — 3 '-nukleotidogidrolaza; KF and; DNA-ase I and DNA-ase II respectively) — the enzymes splitting (depolymerizing) deoxyribonucleic acid; belong to the class of hydrolases and a subclass of hydrolases of phosphomonoesters. Biol, D.'s role consists in their participation in biosynthesis of DNA (see. Deoxyribonucleic acid ), and also in splitting of alien DNA in the course of their catabolism, in participation in digestion, in protection of an organism against alien DNA, in particular from virus. Drugs of DNA-ases are used in quality to lay down. means, and also in laboratory researches. In total D. represent nucleases (see) and on the mechanism of action are phosphodiesterases as they split one of radio bonds of double ether phosphoric to - you. DNA-ases are eurysynusic in bodies and fabrics of live organisms, and D. received from different bodies and biol, liquids of an organism, are not identical on the properties and the mechanism of action. DNA-ase I (KF catalyzes hydrolysis of DNA to mono - oligo-or polynucleotides. DNA-ase II (KF 3.1.4.b) depolymerizes DNA to 3 '-deoxyribonucleotides. Depending on the nature of action of D. subdivide into the ekzodezoksiribonukleaza catalyzing consecutive eliminating of trailer dezoksiribonukleotidny fragments, and the endodeoxyribonucleases splitting internucleotide bonds in molecule DNA.

Dnkaza I's properties from a pancreas are most studied. The optimum of its action is observed in the neutral or alkalescent environment. Enzyme is activated by ions of Mg 2+ also it is inhibited by the citrate, EDTA and other complexing agents connecting bivalent cations. Products of the enzymic hydrolysis of DNA catalyzed by this DNA-ase are oligonucleotides with trailer 5 '-fosforilnymi groups. DNA-ase II has an optimum of pH at 4,5 — 5,5; products of its hydrolysis of DNA are oligonucleotides with 3' - trailer fosforilny groups.

From bacterial and other sources a row endo-DNK-az is allocated. Activity of some bacterial DNA-ases is induced at infection with viruses or phages. So, at E. coli DNK-aznaya activity sharply increases at infection with phages of T2, T4, T5, a lambda, etc. The similar phenomenon is described at infection with viruses of other bacteria, and also some animal fabrics. The special type of D. is represented by the endonucleases with extremely narrow substrate specificity directed to a certain sequence from several nucleotides in molecule DNA which received the name restriktaz. So, a restriktaza of RI from E. coli affects only the sequence of nucleotides guanine — adenine — adenine — thymine — thymine — tsitozin, splitting it at the adenylic rest. Thanks to such narrow specificity of a restriktaza break off molecule DNA only in the few places. At a bacterium owner adenine in the sequence specific to a restriktaza of R1, metilirovan, i.e. character of substrate is changed thanks to what DNA of the owner is steady against action of a restriktaza, and alien DNA is exposed to splitting.

At many microorganisms also the ATP-dependent special group of DNA-ases is described. These enzymes possess the ekzonukleolitichesky action interfaced to disintegration of ATP.

Some of D. hydrolyze as well RNA and are nonspecific nucleases (see). Treat such D., e.g., an ekzonukleaza (phosphodiesterase) of snake poison splitting nucleinic to - you to 5 '-mononucleotides, and the ekzonukleaza from a spleen of animals hydrolyzing nucleinic to - you to 3' - mononucleotides. In the course of ontogenesis activity of DNA-ases in fabrics increases that correlates with a speed of synthesis

of DNA. These observations correspond to data that DNA-ases are necessary for processes replications (see) and DNA repairs (see. Reparation of genetic damages ).

Deoxyribonucleases as drug

In clinic is widely used drug of the pancreatic DNA-ase received from a pancreas of cattle. Lyophilicly dried up pancreatic D. represents inodorous white friable powder, water soluble; in water solutions enzyme is inactivated. Of a termolabiln also does not maintain heating higher than 55 °. It is shown that D. slows down synthesis of virus DNA and reproduction of the DNA-containing viruses detains (adenoviruses, viruses of herpes, viruses of a variolovaccine, etc.). Gets into living cells D., like a nek-eye to macromolecules, way pinocytic (see) also it is isolated in pinotsitozny vacuoles. Believe that therefore D. in the doses significantly exceeding therapeutic does not damage own DNA of living cells, does not slow down its synthesis, does not cause a mutation and does not possess embriotoksichesky and teratogenic action. Hydrolyzes virus DNA as viruses, as well as D., get to cells by a pinocytic and also appear in pinotsitozny vacuoles where their protective fibrous casing is damaged, and virus DNA becomes available to DNA-ase.

With properties D. to depolymerize molecules DNA it is connected also its ability to liquefy pus, viscosity to-rogo is caused by dezoksiribonukleoproteida of kernels of the died leukocytes.

Apply to treatment of a number of the diseases caused by the DNA-containing viruses: herpetic keratitis, adenoviral conjunctivitis and keratitis, acute katar of upper respiratory tracts of the adenoviral nature. It is effective at herpes zoster, at the recurrent herpes simplex forms. Drugs D. use at suppurative processes in lungs for fluidifying of pus and its evacuation. There are data on efficiency of parenteral and submeningeal administration of D. at purulent meningitis. At adenoviral conjunctivitis of D. in fiziol, solution (2 mg/ml) dig in 3 — 4 drops in Nov and on 1 — 2 drops in a conjunctival sac each 3 hours (with a break for the night) within 3 — 4 days. The acute phenomena of adenoviral conjunctivitis usually disappear on 1 — the 3rd day. At an adenoviral and herpetic keratitis and keratouveita solution D. of the same concentration is entered on 0,5 ml daily under a conjunctiva of a sore eye for 2 — 4 weeks and dug in in an eye 3 — 4 times a day. The painful phenomena at a virus keratitis disappear usually in 2 — 3 days after an initiation of treatment Dnkaza's drug, and hypostases, infiltrates, precipitated calcium superphosphates — in 8 — 14 days. At acute katara of upper respiratory tracts of the adenoviral nature solution D. of the same concentration is entered into respiratory tracts in the form of an aerosol within 2 — 5 days (on 2 — 3 inhalations daily).

For treatment of herpetic diseases of skin at adults intramusculary enter on 50 mg of D. into 5 ml fiziol, solution or novocaine (0,25 or 0,5%) each 4 hours for 3 — 10 days.

D.'s use is contraindicated at hypersensitivity to it though D.'s introduction seldom causes allergic reactions.

Release sterile in bottles on 5,10,25 mg with contents not less than 5000 — 7000 EA (activity units) in 1 g. Lyophilicly dried up drug in bottles is stored in the refrigerator (4 °); solution D. (2 mg/ml) keeps activity during 12 hours at cold storage.

Bibliography: Nucleases of microorganisms, under the editorship of A. M. Bezborodov, page 176, M., 1974, bibliogr.; Nucleic acids, the lane with English, under the editorship of I. B. Zbarsky, page 97, M., 1966, bibliogr.; Pearce E. A histochemistry, the lane with English, M., 1962; Sh and-p about V. S t. Nucleases, page 72, M., 1968, bibliogr.

I. B. Zbarsky; R. I. Salganik (pharm.).