PHOSPHORYLASES

From Big Medical Encyclopedia

PHOSPHORYLASES — the enzymes catalyzing reactions of a phosphorolysis, i.e. transfer of glikozilny group to inorganic phosphate or, on the contrary, from a glikozilfosfat on the corresponding acceptor. In this regard F. carry to a subclass gli-koziltransferaz (KF 2.4) of a class of transferases (see).

In addition to the reactions of a phosphorolysis (see) which are carried out at action F. and with the participation of phosphate, enzymatic reactions of splitting of nek-ry connections with the participation of a pyrophosphate are known (see. Phosphoric acids). The enzymes catalyzing such reactions carry the name of pyro-phosphorylases. Genetically caused insufficiency nek-ry F. is the reason of serious hereditary diseases (see). T. are eurysynusic in the nature, they are present at tissues of animals, plants and at microorganisms.

Are most studied by F. polysaccharides (see). Distinguish animal and vegetable F. Pervye reactions of fosforolitichesky splitting of a glycogen catalyze (see), the second — starch (see). One step of action F. on polysaccharide it can be represented by the equation: (Svn10o5) p ~ H3P04 ^ (C6H10O5) p_1-4 ~ Ch-glyukozo-1-fosfat. At the same time it is broken off and respectively becomes isolated and-1 —> a 4-glucosidic bond of polysaccharide. The chain of polysaccharide shortened yaa one glucosic unit is affected


by enzyme with formation of new molecules of glyukozo-1-phosphate again until splitting does not reach to and-1 -» 6 communications, edges is split in already hydrolytic way with the participation of other enzyme — amilo-1,6-glyu-kozidazy (see Glucosidases) then again action F continues., until splitting reaches to following and-1 —> 6 communications etc.

At animals F. hl contain. obr. in a liver and muscles. They meet in two forms — active (phosphorylase and) and poorly active (phosphorylase of Kommersant). The molecule of phosphorylase and consists of four identical subunits, and phosphorylase b ~ of two subunits. Transformation of poorly active phosphorylase b into active phosphorylase and is carried out under the influence of enzyme of a kinase of phosphorylase b (see Kinases) with the participation of ATP and ions of Mg2+. This reaction is resulted by phosphorylation (see) phosphorylases of Kommersant and its dimerization: two

molecules of phosphorylase b connect in one molecule of phosphorylase and:


Balance of this reaction is strongly displaced towards formation of phosphorylase and. Reaction is almost irreversible. However thanks to nali-



the Scheme of the cascade mechanism of activation and deactivation of a phosphorolysis of a glycogen in a skeletal muscle.


a chiya in animal fabrics of special phosphatase of phosphorylase and the active form of enzyme turns into poorly active; at the same time phosphorylase and breaks up to two molecules of phosphorylase £:


Phosphorylase b can turn into phosphorylase and etc. again.

Phosphorylases and and b (KF 2.4.1.1) are emitted in a crystal view from muscles and a liver of animals. Studying of their structure showed that both forms of enzyme contain pyridoxal phosphate (see the Pyridoxine) as prosthetic group (see Coenzymes). Besides, as a part of enzyme there are remains of serine (see) playing an essential role in catalytic activity. At transformation of phosphorylase b into phosphorylase and there is a phosphorylation of the rest of serine, and at transformation of phosphorylase and into phosphorylase b — its dephosphorylation. It is established that in an organism of an animal transformation of phosphorylase b into phosphorylase and accelerates under the influence of adrenaline (see) and a glucagon (see) and is oppressed under the influence of insulin (see). In general regulation of activity F. it is carried out on a helmet to a dnokhm to type (see the scheme) and includes participation, in addition to the called enzymes, and cofactors cyclic 3', 5 '-AMF and protein kinases (KF 2.7.1.37).

^Приведенные on the scheme of reaction provide regulation of a ratio of activities of phosphorylases and and Kommersant in a cell and by that the required speed of transformation of a glycogen into glyukozo-1-phosphate.

The inherited disorders of metabolism of a glycogen in a liver and muscles (see Glycogenoses)


connected with insufficiency phosphorus ilaz are known. In particular, the glycogenosis

of the V type (Mac-Ardla's disease) is caused by insufficiency phosphorus and manholes in skeletal muscles, a glycogenosis

the VI ooze (Gers's disease) — insufficiency of a kinase of phosphorylase of Kommersant in a liver and a glycogenosis of the IX type (a disease of Haga) — lack of a kinase of phosphorylase b in a liver or falloff of its activity. Decrease of the activity F. in skeletal muscles, B6 noted at a hypovitaminosis, is caused by a lack of the pyridoxal phosphate entering as prosthetic group a molecule of enzyme.

Unlike animal phosphorylases vegetable F. represent one active protein. Such F. are allocated from a number of sources (in particular from potatoes) in crystalline state and also contain pyridoxal phosphate in quality of prosthetic group. Other group F., found only in microorganisms, affects disaccharides. Among these F. are known sakharozo-, maltozo-to N of tsellobiozo-phosphorylase. Sakharozofosforilaza (KF 2.4.1.7) catalyzes reaction: sucrose (a-E) - glyukozido-R-V-frukto-zid) + H3P04 ^ Se-B-glyukozo-1-fosfat + D-fructose. Similarly affect a maltozofos-forilaza a maltose and a tsello-biozofosforilaz on cellobiose. At effect of these two enzymes there is an epimerization of a monosaccharide so at one direction of reaction enzymes are specific to a - D - glucose, and at the return — for P-D-glucose.

In animal and vegetable fabrics, and also are available for microorganisms F., the catalyzing reversible tests of splitting of nucleosides in the place of a N-glycosidic linkage; it is a purinnukleozidfosforil-az (KF2.4.2.1) and a pirimidinnukle-ozidfosforilaz (KF 2.4.2.2), the catalyzing reactions purinnukleo-zid - f H3P04 ^ purine + ribozo-1-phosphate (or 2-dezoksiribozo-1-phosphate) and a pyrimidinnucleoside + + H3P04 ^ a pyrimidine + ribozo-1-phosphate (or 2-dezoksiribozo-1-phosphate) respectively. Can be purine bases in nucleosides adenosine, ginoksantin, guanine, and also the nek-ry not natural bases, napr, azaguanine; uracil and thymine can be the pirimidinovy bases in nukleo-zgtda.

In bacterial cells existence of enzyme poly-nukleotidfosforilazy is established (KF 2.7.7.8), catalyzing a reversible test of a phosphorolysis of RNA: RNKP ~

4-H3PO4<“ RNKP-1 + nukleoziddii-phosphate.

Bibliography: Dickson M. and Webb E „Enzymes, the lane with English, page 158, etc., M., 1966; JI and with about in with to and I am N. of the Item and JI and -

N. B vanova. Regulation of effect of muscular phosphorylases, in book: Biol. chemistry, under the editorship of V. L. Kretovich, t. 8, page 110, M., 1975; R about z e N f e l d E. L. and Popov I. A. Glikogenovaya a disease, M., 1979. A. N. Klimov.

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