PHOSPHOROLYSIS

From Big Medical Encyclopedia

PHOSPHOROLYSIS (phosphorus Greek lysis destruction, disintegration) — enzymatic process of splitting of glycosidic linkages in molecules of nek-ry biologically important connections (a glycogen, starch, disaccharides, nucleosides) with participation of inorganic phosphate and formation of phosphoric ethers of monosaccharides. The term «phosphorolysis» was offered by Ya. O. Parnas, to-ry in 1935 opened F. a glycogen (see). In animal fabrics, yeast and bacteria have F. nucleosides, as a result to-rogo phosphoric ethers of a ribose are formed (s:l.) or desoxyriboses (see) and the corresponding nitrogen bases (see the Pirimidinovy bases, Purine bases). In the course of life activity of plants and yeast F. it is carried out during the splitting of starch (see), and at bacteria — during the splitting of disaccharides (see).

On the mechanism F. it is similar to hydrolysis (see) with only that difference that at F. splitting of substrate happens with the participation of phosphoric to - you (see. Phosphoric acids), and at hydrolysis — with the participation of water. The enzymes catalyzing reactions F., received the name of phosphorylases (see). At effect of phosphorylase on polysaccharides (see) — the glycogen, starch — happens consecutive eliminating of the remains of glucose (see) located on the end of a stem nucleus of a molecule of polysaccharide or in places of its branchings to transfer of the glyukozilny rest on phosphoric to - that. As a result of F. molecules of a glycogen can be presented as follows:


In an animal organism F. a glycogen is initial reaction to ways of transformation of a glycogen into glucose in a liver and in lactic acid (see) in muscles (see Glycolysis). T. nucleosides the nukleozidfosfori-manhole proceeds with the participation of enzymes.

Reactions F. are easily reversible since unlike reactions of hydrolysis proceed with little change of free energy. Therefore in vitro synthesis of a glycogen is easily carried out in the system containing glyu-kozo-1-phosphate, the corresponding enzyme and inoculating amounts of polysaccharide. However in vivo formation of a glycogen is carried out in other way — with the participation of enzyme of the gli-kogen-synthase (KF 2.4.1.11) catalyzing transfer of a glucose unit from an uridindifosfatglyukoza on a glycogen.

Bibliography: Parnassus Ya. O. Chosen works, M., 1960; Stepanen

to B. N. Carbohydrates, M., 1968; Whyte A., etc. Fundamentals of biochemistry, the lane with English, M., 1981. A. N. Klimov.

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