PHOSPHOTRANSFERASES

From Big Medical Encyclopedia

PHOSPHOTRANSFERASES — the enzymes catalyzing reactions of transfer of phosphatic groups. T. are found in all live organisms. Important biol. role F. it is connected with their participation in processes of transformation of energy in a cell and in key reactions of cellular metabolism, and also in direct regulation of a number of metabolic processes. Genetically caused insufficiency separate F. is the reason of serious hereditary diseases (see) and the secondary (acquired) disbolism and energy (see). Change of activity or isofermental range (see Isoenzymes) nek-ry F. in blood serum or emergence in blood of activity F., not specific to this fabric, serves valuable, and sometimes and the main diagnostic or predictive character of a disease.

T. belong to the class of transferases (see), and present to a subclass of transferases of phosphorus groups (KF 2.7) the biggest group of enzymes of this subclass covering not only the enzymes catalyzing transfer of phosphate, but also and the enzymes catalyzing transfer of diphosphate (pyrophosphate) and the replaced phosphatic groups (except the nukleotidilny remains, transfer to-rykh is catalyzed by nukleotidiltransferaza). In many cases a donor is the cofactor (coenzyme) attaching transferable phosphatic group.

T. are subdivided into podpod-classes according to the nature of acceptor group, a cut the spirit group (KF 2.7.1), a carboxyl group (KF 2.7.2), nitrogen-containing group (KF 2.7.3), phosphatic group (KF 2.7.4) can carry out a role. A separate subsubclass make F., the reactions of the seeming intramolecular transfer of phosphatic group (KF 2.7.5) operating with regeneration of donors and catalyzing. Difosfotransferaza make a subsubclass of KF 2.7.6; the enzymes catalyzing transfer of phosphatic groups with various deputies (except a nucleoside phosphates) — a subsubclass of KF 2.7.8, and T. with the coupled acceptors, catalyzing transfer of two phosphatic groups of the donor (e.g., ATP) on two various acceptors, make a subsubclass of KF 2.7.9. Fos-fotransferazami in fact are as well the phosphatases (see) catalyzing transfer of the phosphatic remains on hydroxylic ions of an aqueous medium however usually carry such enzymes to hydrolases (see), but not to transferases.

In names F. as donor substance always specify ATP though others can often perform similar function ribo-and dezoksiribonukleozidtrifosfata. However the majority of reactions of transfer of phosphatic groups is carried out with participation of ATP. Such reactions are the reactions proceeding in photosynthesizing membranes of chlorolayers (see Photosynthesis), and also in membranes of bacteria and mitochondrions, followed by oxygen consumption. Are most studied by F., catalyzing transfer of phosphate from ATP on oxygen atoms, nitrogen or sulfur of various acceptors, and known under the name of kinases (see). The reactions catalyzed by kinases of subgroups of KF 2.7.2—4 have big biol. value as thanks to them transfer of energy from one system to another in the form of high-energy phosphatic bonds is carried out (see Vysokoergichesky connections). High-energy bonds are available both in initial here, and in end products therefore these reactions are easily reversible. The kinases relating to subgroup of KF 2.7.1 catalyze transfer of phosphate on hydroxylic group of any sugar or alcohol with bonding, poor energy. In these cases reaction is irreversible since transformation of high-energy communication of ATP into communication poor in energy in a molecule of an end product results.

Majority F., phosphorylating sugar, carries out phosphorylation (see) specifically at one of trailer carbon atoms with formation of ethers on trailer primary spirit group (in situation 5 or 6, and in molecules of ketosugars also in situation 1). Nek-ry kinases, however, make an exception — as a result of their action are formed glikozidfosfa-you.

Among the kinases relating to under - to a subclass of KF 2.7.4, two main enzymes are known (or groups of enzymes), these are nukleozidmonofosfat-kinases (ATP: nukleozidmonofosfat phosphotransferases; KF 2.7.4.4) and nukleoziddifosfatkinaza (ATP: nukleoziddifosfat phosphotransferases; KF 2.7.4.6). Distinction between these two enzymes is in what they use as acceptors nukleozidfosfa-you different degree of a fosforilirovan-nost. In the reactions catalyzed by these F., in quality substances-dono-ditch, except ATP, other nukleozidtrifosfata can work. Extremely active enzyme which is present at all cells — hell-nilatkinaza (ATP: AMF phosphotrance-feraza; KF 2.7.4.3) also catalyzes reaction of nukleozidmonofos-fatkinazny type, but differs in high specificity and affects only derivatives of adenosine.

In subgroup of KF 2.7.6 there are three F., splitting the second pyro-phosphatic communication in molecule ATP so not phosphate, and a pyrophosphate (is transferred see. Phosphoric acids). One of these enzymes — the ribozofosfat-pyrophosphokinase (KF 2.7.6.1) forms specific glikozidpirofosfat — 5-fosforibo-zilpirofosfat, to-ry is the major intermediate compound in biosynthesis of pirimidinovy nucleotides (see Pirimidinovy exchange).

Unlike kinases others F., so-called phosphomutases (KF 2.7.5), do not involve in enzymatic reaction of ATP or others a nucleoside phosphates. Assumed that phosphomutases catalyze an intramolecular transfer of phosphate, moving phosphatic group pz one situation to another in the molecule of substrate. Can be an example of such enzyme a fos-foglyukomutaz (KF 2.7.5.1), catalyzing a reversible isomerization of glyukozo-1-phosphate in a glucocraw phosphate and carrying out the seeming transfer of phosphate in a molecule of glucose phosphate from situation 1 in situation 6. Detailed studying of the mechanism of reaction showed, however, that actually transfer of phosphate is carried out from situation 1 in one molecule in situation 6 in other molecule. Reaction proceeds with transient formation of phosphoenzyme (phosphoryl-enzyme); the phosphatic group in a fos-foferment joins the reactive rest of serine (see).

This type of enzymatic reaction is of great interest. Process can begin only if at the reactionary environment there are traces of glyukozo-1,6-diphosphate, to-ry in this case works as a coenzyme. The catalyzed process represents the act of transfer of phosphate from With, - atom of glyukozo-1,6-diphosphate to C6 atom glyukozo-1 phosphate. Also the new molecule of glyukozo-1,6-diphosphate is as a result formed glyukozo-6-fos-veils. Thus, on each disappeared molecule of glyukozo-1,6-diphosphate one its molecule appears again so total quantity of glyukozo-1,6-diphosphate all the time remains to constants. Apparently, all phosphomutases work in this way: during reaction «coenzyme» turns into a product, and substrate — into «coenzyme», i.e. there is a regeneration, the donor.

In vegetable fabrics it is found unique F. — pyruvate, ortho-phosphate dikinase (ATP: to a feast -

watt, ortho-phosphate phosphotransferase; KF 2.7.9.1.). It is possible to consider that this enzyme catalyzes simultaneous transfer of two phosphatic groups from molecule ATP — one on a molecule of pyruvic acid (see), and another — on an ion of phosphate with formation of a pyrophosphate.

Various F. considerably differ from each other on degree of substrate specificity. In most cases these enzymes are strictly specific in relation to both components of reaction and only in the few cases to one of them. E.g., in reactions of transfer of phosphate from ATP to creatine (see), the creatine kinase (KF 2.7.3.2) proceeding with participation, creatine cannot be replaced with creatinine, L-arginine, D-arginine or L-gpstidinom. ATP cannot be replaced ADF, adenosine-2 '-, adenozpn-3 '-or hell-noznn-5' - phosphate. In back reaction of ADF ATP cannot be replaced. Such high specificity is typical for phosphokinases, however in some cases ATP can replace with other nukleozidtrifosfata; concerning an acceptor of phosphate F. always show high specificity. Pyruvatekinase (KF

2.7.1.40), naira., it is extremely specific to a fosfoyenoliiruvat: any substrate capable to replace it is not found.

In addition to chemical specificity at action on the substances supporting the asymmetric centers, T. find sterichesky specificity and ability to distinguish in symmetric molecules of group, to-rye are chemically identical. So, phosphorylation of glycerin under the influence of a glitserolkinaza (KF 2.7.1.30) gives only

s/g-glitserol-3 phosphate. This asymmetric phosphorylation of a symmetric molecule of glycerin was confirmed with an isotope method and, apparently, is explained by features of the structure of an active center of enzyme allowing to connect substrate only at one orientation though the molecule of substrate is symmetric. The glucokinase of a liver (KF 2.7.1.2) affects D-glucose and D - the semolina storage, but does not affect fructose and many others sugar. Ketogeksoki-naza of a liver (KF 2.7.1.3) phosphorylates D-fructose and some other ketoses in situation 1, but not in situation 6. For nek-ry F., napr, for a fosfo-fruktokinaza (KF 2.7.1.11), replacement of the donor of phosphate in the catalyzed reaction is followed by changes of an optimum pH value: in the presence of ATP the optimum of pH is at 7,8 while in the presence of a nnozintrifosfat (ITF) enzyme finds two maxima of activity — at pH 7,7 and 8,2.

All reactions of transfer of phosphate with participation of ATP demand presence of divalent cations of metals since as active substrate F. only the ATP complex with divalent metals can act. The ATP-magnesium complex is most effective in most cases; ions of Mp2 + and So2 + also have a promoting effect. Possible function of an ion of metal consists in interaction with two phosphatic groups of molecule ATP, to-rye become the leaving groups in substitution reaction: electron density is displaced towards an ion of divalent metal and it facilitates splitting of communication. The ratio of concentration of ATP and ions of Mg2 + strongly influences activity of enzyme. At high concentration divalent cations can be inhibitors, however and ATP in the concentration exceeding concentration of free ions of Mg2+, strongly suppresses activity of enzyme. So, in the based muscle where concentration of ATP is rather high, enzyme a fosfofrukto-kinase, e.g., is inactive. In the course of muscular work when intensive consumption of ATP leads to reduction of its concentration, activity of this enzyme increases; it leads in turn to an intensification of glycolysis (see), and, therefore, and to the strengthened producing ATP. Thus cellular control over carbohydrate metabolism is exercised (see) p synthesis of ATP. Reactants on suljfgid-rilny groups (see), in particular arsenous connections, almost always work as inhibitors F., among to-rykh it is necessary to emit beryllium; its toxic action is explained with the competition to magnesium for linkng with the specific centers F.

T. are very various not only on substrate specificity, but also on other properties: to the relation to coenzymes (see), SH-pea-gentam, in kinetic parameters, stability, and also physical. - to chemical properties. Many F. exist in multiple forms (see Isoenzymes) and possess complex subunit structure; the quantity and properties of isoenzymes can differ depending on a type of cells.

Fiziol. role F. depends on what place is taken by the corresponding enzymatic reaction in a metabolism of an organism. The major representative F. the fosfofruktokinaz can consider. This enzyme in an organism possesses an important regulatory role: on a mode of formation of geksozofosfat process of splitting of carbohydrates (see) can proceed in two main directions — on the way of glycolysis and on a pentozofosfatny way; phosphorylation fosfofruktokinazy fruktozo-6-phosphate predetermines its utilization on the way of glycolysis. Fosfofruktokinaza catalyzes transfer of trailer phosphate from ATP to S-atom of hydroxylic group of fruktozo-6-phosphate with formation of fruktozo-1,6-diphosphate. This enzyme is localized in cytosol and it is found in soluble fraction of the majority of fabrics. For its action ATF2 needs presence of ions of Mg2+ necessary for formation of true substrate, i.e. Mg2 + •". Ions of Mp2 + and So2 + are less effective in this respect. For fosfofruktokinaz from different fabrics high heat stability is characteristic, edges sharply decreases at acidulation of the environment. Fosfofruktokinaza is among allosteric enzymes (see). As well as the majority of such enzymes, it has quite high pier. the weight (weight) and hardly gives in to cleaning. Dependence of the speed of response catalyzed by this enzyme on concentration of substrate indicates the polyvalent nature of regulation of activity of a fosfofruktokinaza.

Other important representative F. the geksokiiaza is (see). Protein kinases (KF 2.7.1.37) are of great interest, to-rye catalyze transfer of phosphatic groups from ATP to hydroxylic groups of the remains of serine or threonine (see) in molecules of proteins-substrates. Important fiziol. the role of these enzymes is connected with their participation in regulation and control of various cellular functions by phosphorylation of the corresponding enzymes with change of their catalytic properties and specificity. Substrate specificity of protein kinases strongly varies; the kinase of phosphorylase (KF 2.7.1.38) and a kinase of piruvatde-hydrogenase belong to highly specific, e.g., to-rye are tsiklo-3', 5 '-AMF-nezavisimymi enzymes. The majority tsiklo-3', 5 '-AMF-zavisimykh protein kinases is specific only concerning the allosteric modulator — a cyclic nucleotide.

Biochemical methods of definition F. are based on properties of specific reactions. E.g., in case of definition of activity of a creatine kinase in blood serum the principle of a method is that in the highly acid environment the formed creatine phosphate breaks up to creatine and inorganic phosphate; the last can be defined colorimetric (see Colorimetry). It is possible as well; *мерять amount of creatine by means of staining reaction with and - naphthol and diacetyl; such is the method based that at addition of blood serum to the incubating medium containing creatine phosphate and ADF creatine is formed on a gain to-rogo judge activity of enzyme.

As during the reactions catalyzed F., the painted or fluorescent connections, for definition of activity F are not formed. these reactions can be accompanied by other enzymatic reactions allowing to receive such connections. So, for definition of activity of a fosfofruk-tokinaza formation of fructose diphosphate is combined with the help of additional enzymes — zymohexases and triozofosfatizomeraza — with oxidation reaction of NAD-N and - glycero-fosfatdegidrogenazoy, to-ruyu register spektrofotometrichesk (see Spektrofotometriya).

Activity in fabrics such F., as a hexokinase, a glucokinase, a creatine kinase and phosphoglucomutase, it is possible to define gistokhy. by the methods based on multi-stage reactions. However these reactions are insufficiently fully developed and so far find only limited application.

Change of activity of a number F., controlling nodal stages of cellular metabolism, plays the main role in an etiology of many hereditary and acquired disbolism. E.g., genetically caused defects of a kinase of phosphorylase, the fos-fofruktokinaza, fosfoglyukomu-Tazy participating in exchange of a glycogen are the reason of various glycogenoses (see), myopathies (see) and a muscular atrophy. Insufficiency of a pyruvatekinase causes deep disturbances in carbohydrate metabolism of erythrocytes (see Enzimopenichesky anemia). At a diabetes mellitus (see a diabetes mellitus) sharp oppression of education glyukozo - 6 - phospha - that is caused by decrease of the activity of a hexokinase that, in turn, is caused by almost total disappearance from fatty tissue of one of isoforms of this enzyme.

Change of activity F. the wedge, the diagnosis can often serve as confirmation, and also to have independent diagnostic and predictive value. So, in cells of kidneys, a liver and fatty tissue insulin induces synthesis of key enzymes of glycolysis: glucokinases, a fosfofruktokinaza and a highly active pyruvatekinase, therefore the content of these enzymes in fabrics at insulin insufficiency, in particular at a diabetes mellitus, forcesno goes down. The creatine kinase (see) is only in muscles, in particular in cross-striped therefore emergence of its activity in blood serum and increase of this activity during some time is a specific character of damage skeletal and cordial muscles. At the progressing muscular atrophy in blood serum activity of a creatine kinase strongly increases. Even more expressed tie of activity of this enzyme in blood is raised observe at a polymiositis. Definition of activity of a creatine kinase in blood serum has important differentsialno - diagnostic value for distinguishing of two groups of myopathies — primary and neurogenic (myasthenias, a muscular atrophy, a family ataxy of Fridrey-ha); neurogenic myopathies unlike primary proceed without change of activity of a creatine kinase.

Bibliography: Dickson M. and Webb E. Enzymes, the lane with English, t. 1 — 3, M., 1982; The Nomenclature of enzymes, the lane with English, under the editorship of A. E. Braunstein, M., 1979;

The enzymes, - ed. by P. D. Boyer, v. 8—9, N. Y. — L.,

1973, P. JI. Ivanov.

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