PHOSPHOPROTEINS

From Big Medical Encyclopedia

FOSFOPROTEYDY (synonym of a fosfo-proteiia) — complex proteins, molecules to-rykh contain the remains of phosphoric acid attached by an ester group to the remains gpdroksiaminokpslot — serine, is more rare than threonine — in a poliiyeptidny chain of these proteins. T. are eurysynusic in various fabrics of all live organisms and make an essential part of proteins (see) cells, playing an important role in cellular metabolism. Caseins (see), proteins of bird's eggs — ovalbumins, vitellin, vitellinin, fosvitin, an ikhtu-lean, and also many major enzymes (see), proteins of biological membranes (see Membranes biological) and cellular kernels belong to phosphoproteins. The remains phosphoric to - you (the phosphatic remains, phosphate ions) F. are chipped off at hydrolysis in alkali and are steady against action to - t. On lability of phosphate in molecules F. in alkaline condition nek-ry methods of their definition are based. For studying F. widely use registration of inclusion of marked inorganic phosphate from (at-32R) ATP or other compounds containing marked phosphorus and eliminating of marked phosphate from F. Phosphoproteins receive by method of sedimentation or a preparative electrophoresis (e.g., an electrophoresis in polyacrylamide gel).

Phosphorylation (see) the remains of serine (see) or threonine (see) in molecules of proteins and their transformation in F. it is catalyzed by group of specific phosphotransferases (see) — the protein kinases operating only on proteinaceous substrates (see Kinases). The main systems stimulating phosphorylation of various proteins depend from cyclic 3', 5' - AMF (tsAMF) and a squirrel of a calmodulin. Dephosphorylation F. catalyze the enzymes of a fosfo-proteidfosfataza capable to chip off phosphate from a native proteinaceous molecule without its preliminary proteolysis.

Phosphorylation of proteins and their transformation in F. represents the main mechanism, by means of to-rogo control of intracellular processes in tissues of mammals from the environment is exercised. Believe that various functions of a cell are controlled by the general protein kinases, fosfoproteidfosfataza and regulatory proteins. In an organism there is the general network of the regulatory ways connected among themselves by phosphorylation — dephosphorylation F., edges allows to coordinate the different metabolic «events» in a cell which are made under the influence of nervous and hormonal incentives.

The most studied system of metabolic regulation by means of phosphorylation — dephosphorylation is the regulation of disintegration and synthesis of a glycogen in muscles at their reduction, and also adrenaline and insulin mediated by change of a condition of phosphorylation of glycogen-phosphoryl-zy (KF 2.4.1.1) and a glycogen synthase (KF 2.4.1.11).

The number of the fosforilirovanny remains of serine in a molecule of fermental protein influences its properties. Phosphorylation of the remains of serine is the simple mechanism allowing to increase considerably the regulatory potential of enzyme. Phosphorylation of one rest of serine can strengthen or have antagonistic effect on effects of phosphorylation of other remains of serine or change the speed of phosphorylation — dephosphorylation of other sites in a molecule of fermental protein. It is shown, e.g., for a piruvatdegidro-genazny complex of mitochondrions: phosphorylation of three remains of serine and - subunits of enzyme promotes its inhibition that prevents oxidation of glucose (see) or its turning into fatty acids (see) as occurs, e.g., at a lack of insulin.

Phosphorylation of various sites of a molecule gives the chance to fermental proteins to react to different fiziol. incentives; in these cases interaction between fosforilirovanny sites often is the mechanism, with the help to-rogo interference of these incentives is carried out. Phosphorylation (covalent modification), influence of allosteric effectors and their interaction with substrates of enzyme allow to carry out integration of nervous and hormonal extracellular information for establishment of necessary activity of a specific metabolic way of in vivo.

Among the known fosfoproteidfos-fataz which are taking part in regulation of metabolism of a glycogen (see) the main is the fosfoproteidfos-fataza I dephosphorylating gli-kogen-synthase (KF 2.4.1.11), a gliko-genfosforilaza (KF 2.4.1.1) and 13-subunit kinases of phosphorylase (KF 2.7.1.38). Fosfoproteidfosfa-taza I, in turn, is phosphoprotein and is activated by phosphorylation. Phosphoprotein is also inhibitor I of this enzyme. Fosfoproteidfosfata-za 1, 2A and 2G have wide substrate specificity and carry out dephosphorylation not only the enzymes participating in exchange of a glycogen in a liver and muscles but also a pyruvatekinase (KF

2.7.1.40), atsetil-KOA — carboxy - manholes (KF 6.4.1.2), gidroksimetil-glutaril-KOA — reductases (KF 1.1.1.88), regulating thus a gluconeogenesis, synthesis fat to - t and cholesterol (see).

In tissue of a brain of mammals several tens F is identified. Apparently, nek-ry of them take part in processes of training and storing (see Memory). Essential role defined F. in functioning of synaptosomes or synoptic vesicles it is connected with ability F. to remain in the changed state after implementation of training. T. a brain on their regional distribution belong to three categories: one F. are evenly distributed in departments of a brain, others are widespread widely, but are distributed unevenly, and the third are found only in limited specific structures of a brain. Various F. a brain are substrates for the tsAMF-dependent protein kinase and protein kinases dependent on Sa2+-kalmodulina and Sa2+-fosfolipida. Phosphorylation of the major proteins of a brain and their transformation in F. occurs at depolarization (see), stimulations of nerves (see Excitement), and also under the influence of certain neurotransmitters (see Mediators of a nervous system).

There are data that phosphorylation of five remains of serine and threonine on the S-end of a polypeptide chain of visual protein of rhodopsin (see) and its transformation in F. plays a part in regulation of adaptation of an eye to light and darkness (see visual adaptation).

Bibliography: Lisovskaya N. P. and

Livanov N. B. Phosphoproteins, M., 1960; Cohen P. The role of protein phosphorylation in neural and hormonal control of cellular activity, Nature (Lond.), v. 296, p. 613, 1982, bibliogr.; Rout-tenberg A. Anatomical localization of phosphoprotein and glycoprotein substrates of memory, Progr. Neurobiol., v. 12, p. 85, 1979, bibliogr. H. V. Gulyaeva.

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