POLYSACCHARIDES

From Big Medical Encyclopedia

POLYSACCHARIDES (synonym: glycanes, polyoses complex of sugar) — the high-molecular carbohydrates having great biological value, molecules to-rykh are constructed not less than of 10 monosakharidny remains connected with each other by glycosidic linkages. At animal and vegetable organisms glycogen (see) and starch (see) — the major reserve connections; mucopolysaccharides (see), cellulose (see), etc. perform structural functions. Many biologically active agents — heparin (see), hyaluronic acids (see), etc. — are also P. Chrezvychayno an important role in food of the person play grain products (see), starch, vegetables (see), pectic substances (see), sugary products (see), carbohydrates (see), fruit (see), bread, bakery products (see), consisting generally of P. or being blank Items. Disturbance of exchange of separate P. at the person leads to development of a serious illness (see. Glycogenoses , Glikozidoza , Hereditary diseases ).

Items are eurysynusic in the nature and make the ground mass of organic matter on Earth. P. are divided by the origin on animals — zoopolysaccharides, vegetable — phytopolysaccharides and polysaccharides of microorganisms.

From the point of view of a chemical structure of P. are condensation polymers which are formed as a result of consecutive accession to each other monosaccharides (see) with eliminating of water (see. Polymerization ). General formula of the majority of polysaccharides C n H 2m O m . Pier. the weight (weight) varies from several thousand to several million.

On P.'s structure are divided into the gomopolisakharida constructed of the remains of one monosaccharide, napr from glucose — a glycogen, starch, cellulose, etc., and the heteropolysaccharides constructed of the remains of various monosaccharides, napr, a glucomanna-ny, hemicelluloses, hondroitinsulfata, etc. Poly-glikozidnoy P.'s chains are divided by a structure on linear (e.g., amylose, cellulose) and branched out (a glycogen, amylopectin). P.'s variety is caused by the fact that the monosakharidny remains can be in their molecules in pyranoheat or the truck-noznoy forms and to have alpha or a beta configuration of the glikozidny centers, and each of these remains can be connected by a glycosidic linkage with any hydroxylic group of the next monosakharidny rest. Items are molecular composition of conjugate biopolymers which, except carbohydrate, contain proteinaceous (see. Glycoproteins ) or lipidic (see. Glycolipids ) components. There is no systematic chemical nomenclature of P., the rational principle is the basis for existing P.'s nomenclature: the termination «-An» is added to the name of the monosaccharide making P. or to the name of the last monosakharidny rest: D-glucan, L - arabino - D - galactan, etc.

P. — usually colourless amorphous substances which do not have sweet taste; they share on water-insoluble and soluble which in water easily bulk up and form the viscous colloid solutions having optical activity. Even in polar organic solvents (formamide, methanol, ethanol, etc.) P. badly rastvorima. P.'s most is rather steady in alkaline condition, and to-tami or specific enzymes are hydrolyzed to monosaccharides (see) and oligosaccharides (see).

The molecule P. contains only one recovering free hemiacetal hydroxyl therefore the recovering properties at P. are shown very poorly. Free hydroxylic groups P. can atsilirovats I ialkilirovat-sya, at oxidation iodic to - that P. form aldehydic groups.

For individual P.' allocation use methods of extraction, sedimentation (see. Sedimentation methods ), dialysis (see) and ultrafiltrations (see), chromatography (see), electrophoresis (see) and ultracentrifuging (see). The structure and P.'s structure are defined physical. - chemical methods, napr, method of the X-ray crystallographic analysis, spectroscopy 13 S-YaMR (see. Nuclear magnetic resonance ), chemical methods, napr, methylation, peryodatny oxidation, partial hydrolysis, and also methods of the analysis of oligosaccharides.

P.'s biosynthesis in a human body and animals is carried out by hl. obr. by an enzymatic transglycosylation with participation of nukle-otiddifosfatsakhar, the monosakharidny rest to-rykh is postponed to the growing polisakharidny chain, phosphates of sugars can also act as donors of the glikozilny remains. Heteropolysaccharides can be synthesized with participation of lipidic and nucleotide carriers which form the repeating links under the influence of enzyme of a polymerase connecting in a molecule of heteropolysaccharide. Branched gomopolisakharida are formed of linear P. by intramolecular enzymatic reorganization.

In a human body and animals reserve and nutritious P. are split to monosaccharides or phosphates of sugars of hl. obr. under the influence of phosphorylases, and also endo-and ekzoamilaz (see. Carbohydrate metabolism ).

Items have antigenic properties. These properties P. highly depend on their molecular structure. Special value for medicine has studying of bacterial polysaccharides (see. Bacteria ) and lipopolisakharid (see).

Bacterial P. have pronounced antigenic properties: at introduction to an organism they induce immune responses and react with the corresponding antibodies. The immune response on P. is characterized by a number of the features distinguishing it from an immune response by antigens of the polypeptide nature. Items cause products of antibodies in experimental animals already at single introduction of a small dose (a share of microgram); synthesis of antibodies begins very much early — in three days after immunization, and are usually synthesized an antibody both IgM-, and an IgG-class. Antibody formation in the first days after immunization occurs very intensively, and then decreases and proceeds at a low level for a long time. Bacterial P.' most (polysaccharides of pneumococci, S. typhi Vi-antigen, specific polysaccharides of meningokokk) are a thymus gland-nezavisi-mymi, t. e. antibodies to them are produced by V-lymphocytes without participation of T lymphocytes. At the same time products of antibodies to these antigens are controlled by special subpopulation of lymphocytes — T-supres-sorami.

To polisakharidny antigens it can be rather easily created immunol, tolerance, and it is often caused by emergence and functioning of T-suppressors.

The expressed immunol, bacterial P.' activity formed a basis of their use in medical practice as so-called chemical vaccines. Vaccines from polysaccharides of a cell wall of pneumococci, meningokokk, S. typhi, Haemophilus influenzae have high performance.



Bibliography: Kochetkov N. K., etc. Chemistry of carbohydrates, M., 1967; M about to p e of the Tax Code about A. I. Primary and secondary immune response of mice on polisakharidny antigens of meningokokk of serogroups And yes With, Zhurn, mikr., epid, and immun., No. 4, page 72, 1980, bibliogr.; Stacey M. and B and republics of e r Page. Carbohydrates of living tissues, the lane with English, M., 1965; Stepanenko B. N. Chemistry and biochemistry of carbohydrates (polysaccharides), M., 1978; G about t s with h-1 i with h I. and. o. The immune responses to bacterial polysaccharides in man, in book: Antibodies in human diagnosis and therapy, ed. by E. Haber and. Century of M. Krause, p. 391, N. Y., 1977, bibliogr.; Whistler R. L. a. Smart C. L. Polysaccharide chemistry, N. Y., 1953.


V. K. Gorodetsky; H. A. Kraskina (of).

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