SIALIC ACIDS

From Big Medical Encyclopedia

SIALIC ACIDS — the drawn-up derivatives of neuraminic acid, are a part of glycoproteins, glycolipids (gangliosides), mucins and other glycoconjugates. Biol. S.'s role to. is defined by their participation in formation of specific properties of physiologically active uglevodsoderzhashchy connections. S.'s maintenance to. in blood is additional diagnostic test at nek-ry inflammatory diseases — arthritises (see), polyarthritises (see), pseudorheumatism (see), etc., characterizing extent of inflammatory process. Genetically caused insufficiency of enzyme of a neuraminidase (sialidoses; KF 3. 2. 1. 18) serves as an origin of hereditary diseases of accumulation of sialidoses. In not acylated state neuraminic acid (see) is unstable substance and in the nature does not meet.

Free S. to. in an organism of animals and the person are found in very insignificant quantities. As a rule, they are a part of various oligosaccharides (see), glycolipids (see) — gangliosides (see) and glycoproteins (see). The glycoproteins containing a large number of S. to., call sialo-glycoproteins. Polymer of one of S. is found in bacteria to. — N-atsetilneyraminovoy to - you — so-called kolominovy to - that.

Page to. distinguish depending on type of acylic radicals (usually acetyl - or glikolil-), their number and the nature of communication (N-or O-). By means of chemical synthesis S. are received to., not meeting in the nature, napr, benzoyl - iropionil-, formyl - suktsinilneyraminovy to - you, etc.

Pure S. to. represent colourless crystals, easily water soluble, restrictedly soluble in methanol and insoluble on air; they are unstable in solutions of alkalis and to - t, during the heating collapse with decolourization. Page to. are strong to-tami and recover liquid of Felinga.

S.'s biosynthesis to. in an organism of animals and the person begins with phosphorylations (see) M-atsetilmannozamina under the influence of of the same name kinases (see). Fosforilirovanny N-atsetilmannozamin and fosfoyenol-pyroracemic to - that are biosynthetic predecessors

of S. to. Under the influence of specific N-atsetilneyraminat-synthase (KF 4. 1. 3. 19) they turn into N-atsetilneyraminovuyu to - that. Of it by a direct enzymatic hydroxylation it is formed N-gli-kolilneyraminovaya to - that. Except oxygen, this reaction demands presence ascorbic to - you and ions of Fe2+. Donor of anion acetic acid (see) — acetyl — at S.'s education to. serves atsetil-KOA. Enzymes atsetil-KOA: N-atsetil-neyraminat - 4 - O-acetyltransferase (KF 2. 3. 1. 44) and atsetil-KOA: N-atse-tilneyraminat 7 (or 8) - 0-acetyls-transferases (KF 2. 3. 1. 45) participate in the corresponding S.' education to. — N-and O-diatsetil-and N - acetyl - About - diatsetilneyraminovoy to - t. It is established that these transformations can happen after inclusion of N-atsetilneyraminovoy to - you in glycoproteins. S.'s accession to. to a molecule of glycoconjugate occurs after its activation by cytidinemonophosphate (TsMF). Education TsMF-sialovykh to - t catalyzes atsilneyraminat-tsiti-dililtransferaza (a Tsmfsialat-sin-taza; KF 2. 7. 7. 43). This enzyme is not specific concerning different S. to. S.'s transfer to. from the activated TsMF C. to. it is carried out with the participation of specific sialiltrans-feraz (KF 2. 4. 99. 1).

N-atsetilneyraminovaya and N-gli-kolilneyraminovaya to - you are split under the influence of zymohexase N-acylneuraminic to - you (KF 4. 1. 3. 3) on the corresponding N-acyl-mannosamine and pyroracemic to - that. The diacylated S. to. almost are not split by this enzyme.

From molecules of the substances C. supporting them to. are chipped off under the influence of a neuraminidase. Time of circulation in a blood-groove of nek-ry blood proteins (ceruloplasmin, о^-гл about an ulin, etc.) and nek-ry hormones (a chorionic gonadotrophin, follicle-stimulating and luteinizing hormones, etc.) after eliminating from their molecules C. to. it is sharply reduced. Asialoglikoproteida have on the end of a carbohydrate chain, as a rule, galactose (see) that does possible their absorption to cookies, a cut, in turn, is provided with the specific receptors containing S. to. Loss biol. activities nek-ry hormones after their desialirovaniye explain them with disappearance from a blood-groove now. Duration of circulation in a blood-groove of nek-ry blood cells also decreases after removal from their surface of S. to. Assume that process of aging of erythrocytes is connected with reduction of number of S. to. in their cover.

It is established that S. to. create the high density of a negative charge on molecules of glikoprotets-d and mucins and by that cause the extended, rod form of their molecules, thanking cover the secrets of mucous membranes of respiratory tracts, intestines and genital tract differing in high content of sialoglikoproteid, have high viscosity that provides protection of mucous membranes against penetration of bacteria, and also against mechanical and chemical damages. Page to. as a part of glycoproteins of a secret of mucous membranes of a genital tract play an essential role in process fertilisations (see). Viscosity of a secret in a neck of uterus decreases only during an ovulation, facilitating access to spermatozoa to an ovum. Page to. are an important component of a brilliant zone (zona pellucida) of an ovum of mammals: after S.'s removal to. spermatozoa cannot get in an ovum. Page to. substantially define ability of cells to adhesions (see). Assume that S. to. mask the remains of the sugars which are antigenic determinants in glycoproteins. S.'s removal to. from glycoproteins or from a surface of cells raises their immunogenicity. S.'s maintenance to. in blood sharply raises at many acute and hron. inflammatory diseases.

Excess excretion of sialooligosakharid with urine is observed at sialidoses — group of the diseases caused by insufficiency of a neuraminidase (sialidoses), the enzyme which is chipping off the trailer remains of S. to. from various substances supporting them. Sialidoses represent the hereditary diseases of accumulation which are transferred on autosomes - but - recessively to a mode of inheritance. Characteristic a wedge, signs of sialidoses are myoclonic spasms, emergence on an eyeground of a spot like «cherry stone», the progressing blindness. Distinguish sialidoses of type 1, a wedge which picture is characterized by lack of mental retardation and signs of a dismorfiz-m, and the sialidoses of type 2 which are characterized by the mental retardation and dismorfichesky signs reminding a dismorfizm at a syndrome Gurler (see. Gargoilizm ). The maintenance of separate sialooligosakharid in urine of patients with sialidoses exceeds norm more than by 100 times. Identification of sialooligosakharid in urine by means of thin layer chromatography (see) use for preliminary diagnosis of a sialidosis. The final diagnosis can be made only after establishment of insufficiency of a neuraminidase in leukocytes and culture of skin fibroblasts.

Also cases of a sialuriya when at the patient with urine the huge number of S. was allocated to are described. (to 7 g a day) in the form of free N-acetyl-eeyraminovoy to - you.

By the most sensitive and specific methods of definition of S. to. in biol. material (blood serum, synovial fluid, etc.) the resorcinol method of Svennerkholm and a method of definition of S. are to. with thiobarbituric to - that.

At S.'s definition to. by Svennerkholm's method to the solution containing S. to., add resorcin, salt to - that, and maintain copper sulfate within 15 min. on the boiling water bath. Intensity of the developing blue coloring is directly proportional to the maintenance of €. to. in test also decides by a fotometrirovaniye on the red light filter (see. Photometry ). A method of definition of S. to. with thiobarbituric to - that it is based on their oxidation by periodate of sodium and definition of intensity of the coloring developing as a result of interaction formed beta and formylpyroracemic to - you with thiobarbituric to - that. The painted solution is kolorimetrirut at 549 nanometers.



Bibliography: Tsvetkova I. V. Neuraminic acid and its value in an organism, Vopr. medical chemical. t. 7, No. 1, page 1, 1961, bibliogr.; Lowden J. A. a. O’Brien J. S. Sialidosis, review of human neuraminidase deficiency, Amer. J. hum. Genet., v. 31, p. 1, 1979; Schauer R. Chemistry and biology of the acylneurami-nic acids, Angew. Chem., Bd 85, S. 128, 1973; Sharon N. Complex carbohydrates, Their chemistry, biosynthesis and functions, Reading, 1975.


I. V. Tsvetkova.

Яндекс.Метрика