From Big Medical Encyclopedia

NUCLEOTIDASES — the enzymes catalyzing splitting of phosphomonoradio bonds in mononucleotides with formation of nucleosides and inorganic phosphate; belong to the class of hydrolases and a subclass of hydrolases of phosphomonoesters (KF 3.1.3). Biol, N.'s role is connected with their participation in cellular metabolism nucleic acids (see) and their predecessors. On the nature of catalytic action all N. are the phosphomonoesterases splitting radio communication phosphoric to - you with the participation of a water molecule.

Depending on at what carbon atom (5 '-or 3 '-) in a carbohydrate component of the attacked nucleotide the fosforil-ny rest is located, N. are divided into three groups: 5 '-nukleotrshchazy, Z '-nucleotidases and 5' (Z') - the nucleotidases hydrolyzing both types of mononucleotides.

5 '-Nukleotidazy (5th '-ribonucleotides-phosphohydrolases; KF are eurysynusic in the nature.

Enzymes from plants, tissues of animals and the person, snake poison, yeast and bacteria are allocated and described. Enzymes from different sources have nek-ry general properties; at the same time noticeable distinctions in their substrate specificity, and also in catalytic, physical and chemical properties are found. The most general properties 5' - nucleotidases is their activation and inhibition ions of nek-ry metals. In most cases cations of Sa2+, Mn2+, Ni2 + activate these enzymes, a Zn2+, Cu2 + and kompleksobrazuyushchy (chelating) agents are their inhibitors. Pier. the weight (weight) 5 '-nucleotidases vary from 10 000 (enzyme from poison of a cobra) to 237 000 (enzyme from a hypophysis of cattle). Molecules separate 5' - nucleotidases can consist sh several subunits and often find allosteric type of regulation. The active center nek-ry of these enzymes contains Zn2+.

In many fabrics 5 '-nucleotidases are present at a type of multiple forms — isoenzymes (see). So, for 5' - nucleotidases of a liver of various animals, including and the person, substrate specificity and kinetic properties differ depending on cellular localization of enzyme. Enzyme from lysosomes, e.g., has unusual substrate specificity, hydrolyzing, in addition to 5 '-nukleozidmonofos-fatov, 2 '-and Z '-nukleozidmonofosfa-you. Cytoplasmatic enzymes have narrower substrate specificity: nek-ry are most active concerning 5 '-inozinmo-nofosfata and 5' - guanozinmonofosfa - that, others act with hl. obr. on a misinformation oxythymidinemonophosphate and uridine-monophosphate. In a liver the most part 5 '-nucleotidases is associated with membranes. Several isoenzymes 5' - nucleotidases are present at nervous tissue; 5 '-nukleotidaznaya activity is found in white and gray matter of a brain, and the highest activity — in bark, a cerebellum and a spinal cord. It is shown that activity 5 '-nucleotidases is strongly reduced in comparison with norm in the demyelinated sites of a brain at the patients having multiple sclerosis. Localizations 5' - nucleotidases in cells of an endothelium of coronary capillaries and small vessels of heart attribute great value in connection with an estimated role of adenosine as fiziol. regulator of coronary circulation. High activity 5 '-nucleotidases (3-limfotsi-tov prevents accumulation toxic for lymphoid cells dezoksi-ATF at hereditary week about hundred that chno with ti hell but z ying de Z of amine z y (KF whereas function of the T lymphocytes possessing low-active 5' - nucleotidase, at this hereditary defect is broken because of suppression of synthesis of DNA in them dezoksi-ATF.

The enzymes hydrolyzing nuk-leozid-Z '-monophosphates (Z '-ribonuk-leotid-phosphohydrolases; KF, are studied less, than 5 '-nukleo-tidazy. The hydrolases having substrate specificity in relation to Z' - to ribonucleotides, are inherent to hl. obr. to vegetable fabrics. These enzymes for manifestation of their activity need ions of Zn2+.

In cells E. coli infected with T-even bacteriophages activity appears new Z '-dezoksiribo-nukleotidaznaya. Induced by a phage Z '-nucleotidase on the kinetic properties is very similar with bacterial 5 '-nuk-leotidazami.

Many microorganisms produce tsiklo-2', Z '-ribonucleosides-phosphodiesterases (KF having Z '-nukleotidaznoy activity. The similar enzymes having two active centers different for hydrolysis of cyclophosphodiesters and phosphomonoesters are emitted from various Enterobacteriacea, Bacillus subtilis, Vibrio alginolyticus. Bacterial enzymes are similar among themselves concerning an optimum of pH, thermosensitivity, activation and inhibition ions of metals and are strictly specific to Z '-to ribonucleotides. These enzymes can participate together with RNA elements in a catabolism of RNA, affecting oligonucleotides with trailer 2', Z '-cyclonucleotides and consistently splitting the last to Z' - mononucleotides and further — to nucleosides and ortho-phosphate.

In animal and vegetable fabrics are found having wide substrate specificity 5' (Z') - the nucleotidases (KF participating in degradation 3 '-both 5 '-ribo-and deoxyribonucleotides. These enzymes are least active in fabrics with resistant, constant cell populations — in a brain, heart, skeletal muscles. The fabrics consisting of short-lived cells (e.g., blood), on the contrary, are characterized by a superactivity of these enzymes. 5' (Z') - Nucleotidases are activated by allosteric effectors and carry out a regulatory role in exchange nucleinic to - t. It is supposed that with 5 '-nukleotidaznoy activity connected delay of synthesis of DNA; Z '-nukleotidaznaya activity participates in a reutilization 3 '-the nucleotides which are formed as a result of action nucleases (see).

Majority of methods of definition: N.'s activities it is based on colorimetric (see. Colorimetry ), spektrofotometrichesky (see. Spektrofotometriya ) or isotope determination of amount of the inorganic phosphate which is formed as a result of hydrolysis of nucleotides.

See also Enzymes .

Bibliography: Dorofeyev G. I., Kozhemyakin JI. And. and Ivashkin V. T. Cyclic nucleotides and adaptation of an organism, JI., 1978, bibliogr.; Fedorov N. A. Biological and clinical value of cyclic nucleotides, M., 1979; The enzymes, ed. by P. D. Boyer, v. 4, p. 337, 355, N.Y. — L., 1971; F r i t z o n P. Regulation of nucleotidase activities in animal tissues, in book: Advans. in enzyme regulation, ed. by G. Weber, v. 16, p. 43, Oxford a. o., 1978.

P. L. Ivanov.