GLUCOSIDASES

From Big Medical Encyclopedia

GLUCOSIDASES (D - glucosides-glycihydrolases; KF 3. 2. 1) — group of the enzymes belonging to the class of hydrolases and hydrolyzing a glucosidic bond in molecules of simple glucosides, oligo-and polysaccharides. Genetically caused insufficiency of certain representatives of G. is the reason of many hereditary diseases of the person.

The reaction catalyzed by G. leads to formation of free glucose and alcohol:

where R — agglucon, i.e. the part of a molecule connected by a glucosidic bond with the glyukozilny rest, the Aglyukonovy part of molecules of the substrates attacked by G. can be various oxycompounds of fat, aromatic and carbocyclic ranks, and also glucose and its derivatives. Except reaction of hydrolysis, G.'s most catalyzes also reaction of a transglyukozilirovaniye. Are specific in relation to a configuration of a glucosidic bond and on this basis also beta glucosidases share on alpha.

Alpha Glucosidases are eurysynusic in the nature and are found at bacteria, the lowest mushrooms, plants, animals and the person. Activity of alpha glucosidases is found in mammals and the person in all bodies, fabrics and biol, liquids.

Beta Glucosidases are found at microorganisms, plants, mollusks, mammals and the person.

Alpha Glucosidases split as synthetic alpha glucosides (phenyl - para-nitrofenil-, 4 methyl umbelliferil - alpha D - glucopyranosides, etc.), and natural substrates (a maltose and its polymeric homologs, sucrose, trehalose and a row other). Thanks to ability of alpha glucosidases to split a maltose them often call maltases. From some biol, sources of alpha glucosidase are allocated in a high cleaning state. They represent well water soluble squirrels who are not demanding for manifestation of the activity of presence of cofactors.

The molecular weight of alpha glucosidases varies over a wide range depending on a source of enzyme (from 60 000 to 300 000). In some cases the subunit structure of alpha glucosidases is established. Linkng of a molecule of substrate with their active center is carried out by means of hydroxylic groups at the 2, 3, 4 and 6 carbon atoms of the trailer rest of glucose.

It defines absolute specificity of alpha glucosidases in relation to a gluconic part of substrate. The inhibitors, general for all alpha glucosidases, are glucose — an end product of the reaction catalyzed by alpha glucosidases and also gluconolactone, mesoerythritol and Tris.

Optimum pH values for alpha glucosidases are or in area from 4 to 5 (acid alpha glucosidases), or from 6 to 7 (neutral alpha glucosidases). Acid alpha glucosidases are localized in lysosomes, neutral — in microsomes and a hyaloplasma. Fiziol, value of alpha glucosidases of a mucous membrane of a small intestine consists in hydrolytic decomposition to glucose of the oligosaccharides getting to an organism with food or formed as a result of starch hydrolysis of food under the influence of alpha amylase (see. Amylases ). Deficit or lack of alpha glucosidases (maltases) in a mucous membrane of a small intestine of the person leads to the diseases connected with intolerance of disaccharides (see. Malabsorption syndrome ). At the same time observe the following symptoms: spasms, diarrhea, abdominal pains, release of disaccharides with a stake, in more hard cases — damage of a liver and kidneys. Fabric alpha glucosidases participate in intracellular splitting of a glycogen and products of its enzymic hydrolysis to glucose. Absence or insufficiency in bodies and tissues of the person of the acid lizosomalny alpha glucosidase called also by gamma amylase leads to the most severe form of a glycogenosis — a disease to the Pomp (see. Glycogenoses ).

beta Glucosidases (KF 3. 2. 1. 21) catalyze hydrolysis of a beta glucosidic bond in natural and synthetic beta glucosides and various di - and oligosaccharides (cellobiose, a laminaribioza, gentiobiose etc.). Unlike alpha glucosidases linkng of a molecule of substrate with an active center of beta glucosidases is carried out by means of hydroxylic groups at the 2, 3 and 4 carbon atoms of the rest of glucose thanks to what beta glucosidase along with beta glucosides is capable to split 6-dezoksibeta-glucosides and beta D - ksilopiranozidy. Many properties of beta glucosidases are similar to similar properties of alpha glucosidases (lack of cofactors, close values of the optimum sizes pH, structure of inhibitors).

Methods of definition of activity alpha and beta glucosidases, applied in laboratory practice, are also similar: during the use of natural substrates definition of activity of G. is based on measurement (e.g., a glyukozooksidazny method) amounts of the glucose which is formed as a result of enzymatic reaction. During the use as substrates phenyl - para-nitrophenyl or 4-metilumbelliferil-glucosides definition of activity of G. comes down to measurement of amount of the formed phenol, para-nitrophenol or a metilumbelliferol respectively.

In a human body beta glucosidase with an optimum of pH 4,0 is found. As specific substrate for this enzyme serves beta glucocerebroside thanks to what this beta glucosidase received the name acid beta glyukotserebrozidazy. Unlike all famous G., acid beta glyukotserebrozidaza represents the multicomponent enzyme consisting of the labile high-molecular protein having catalytic properties and which is strongly connected with a membrane and the thermostable, not connected with a membrane low-molecular effector of the glikoproteidny nature. Each of components of this enzymatic complex separately has no activity of beta glucosidase, and only the interaction of catalytic and effector proteins happening in the presence of acid phospholipid leads to education active beta glyukotserebrozidazy. Absence in bodies and tissues of the person of one of components of this complex is the reason of a severe hereditary form of a glycolipidosis — diseases to Gosha (see. to Gosha disease ).

See also Hydrolases .



Bibliography: Badalyan L. O., Tabolin V. A. and Veltishchev Yu. E. Hereditary diseases at children, M., 1971; Biochemical diagnosis of hereditary diseases, under the editorship of E. L. Rosen-felda and T. T. Berezov, page 46, M., 1974; Kochetkov N. K. ides of river. Chemistry of carbohydrates, M., 1967; But M. of W. a.o. Glucoce-rebrosidase, reconstitution of activity from macromolecular components, Biochem. J., v. 131, p. 173, 1973; R e e s e E. T., M a-g u i r e A. H. a. P a r r i s h F. W. Glu-cosidasesand exo-glucanases, Canad. J. Biochem., v. 46, p. 25, 1968.

D. M. Belenky.

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