GLUCOSE

From Big Medical Encyclopedia

GLUCOSE (Greek glykys sweet) — a monosaccharide, aldohexose, C 6 H 12 O 6  ; substance, molecules to-rogo carry out a role of a biofuel in one of the main power processes in an animal organism — in the course of glycolysis (anaerobic splitting of glucose to milk to - you with formation of ATP). Is oxidized also in a pentozny cycle to CO 2 and waters, generating energy for some sintetazny reactions. Performing power function, G. plays also an important structural role in an organism of animals, plants and in microorganisms, being a component structural polysaccharides (see) and glycoproteins (see).

Exists as well as all monosaccharides (see), in the form of two optical antipodes of I and II):

The monosaccharide, most widespread in the nature, is D-glucose (grape sugar, or the dextrose) for the first time allocated in 18 century. In a stand-at-ease D-glucose contains in honey together with fructose (see), in fruits, flowers and other bodies of plants, and also in animal fabrics — in blood, a lymph, cerebrospinal liquid, tissue of a brain, cordial and skeletal muscles etc. Urine of healthy people contains very small amount of G., a cut it is not found in the usual clinical analysis.

Are widespread in the nature containing. oligosaccharides (see) — malt sugar, lactose, saccharobiose, various glycosides (see) and polysaccharides — starch, a glycogen, cellulose, a dextran, etc.

receive D-glucose starch hydrolysis of 0,25 — 0,5% of HCl under pressure of 1 — 2 atm.

Tautomeric forms of glucose.

In solutions G. exists in the form of 5 tautomeric forms (see fig.) — α-and β-glucopyranoses with six-membered ring (37 and 63% of all dissolved G. respectively), α-and β-glucofuranoses (with pentatomic ring) and in the form of an open (acyclic) form with free aldehydic group — al form (in solution these forms G. are in shares of percent).

α-and β-forms (both pyranoses, and furanoses) differ in a spatial relationship of a hemiacetal hydroxyl (in formulas it is led round by a dotted line).

α-D-glyukopiranoza in the form of crystal monohydrate is besieged from water solutions at a temperature below 50 °, t°pl 83 °. Anhydrous alpha D - glucopyranose turns out at crystallization at a temperature over 50 ° (but lower than 115 °); t ° pl 146 ° and ud. rotation + 112,2 °. beta D - glucopyranose crystallizes at a temperature over +115 °; t ° pl 148 — 150 ° and ud. rotation +19,3 °.

L-glucose was received synthetic. However some of its derivatives which are found in the nature are known. Treats them N-atse-til-glyukozamits — a construction component of penicillin. L - gluco - for, unlike D-glucose, it is not capable to be fermented.

Mutual transition of tautomeric forms G. is followed by change ud, rotations — mutarotation (see).

Researches of conformation of a molecule G. showed that the molecule D-glucose exists in chair conformation of S-1 (see. Monosaccharides ). In β-D-glyukoza's molecule all massive groups — hydroxyls and oxymethyl group — are in the equatorial situation that gives to a molecule conformational stability. For this reason beta D - glucose prevails in equilibrium Solution. Conformational stability of G. in comparison with other monosaccharides is probably the reason of a wide spread occurance of this sugar in the nature as reserve (in polysaccharides) and transport carbohydrate.

Very easily is oxidized oxides and hydroxides of heavy metals that is the cornerstone of qualitative tests on G., in particular and at a wedge, the analysis: e.g., G.'s definition by means of hydrated copper oxide — Trommer's test (see. Carbohydrates ), main bismuth nitrate (Bettger's test), ammoniac solution of silver oxide (silver mirror reaction). In the conditions of these reactions (oxidation in alkaline condition) the molecule G. is split on fragments with shorter carbon chains and forms a number of oxidates, such as milk or ant to - that, etc. At G.'s oxidation bromine forms monobasic gluconic acid (see); more vigorous oxidation (HNO 3 ) gives double-base sugar to - that. At G.'s oxidation on S-6 glucuronic acid turns out (see. Hexuronic acids ).

Specific oxidation of G. in gluconic to - that is catalyzed by enzyme glucose oxydas (KF 1. 1. 3, 4). As at the same time only D-glucose is oxidized, glucose oxydas is widely applied in biochemical, and chemical analyses since gives the chance selectively to define G. in mixes with other monosaccharides (see. Gorodetsky methods ).

At G.'s recovery hexatomic alcohol turns out sorbite (see). At substitution by the radical of hydrogen atom in a hemiacetal hydroxyl of G. glucosides are formed. Substitution of hydrogen atom at S-2 an amino group leads to education glycosamine (see).

In an organism is an important energy source. Full oxidation of G. goes on the equation:

With 6 H 12 O 6 + 6O 2 —> 6CO 2 + 6H 2 O + 686 kcal/mol.

A considerable part of the marked-out energy accumulates in ATP and similar to it vysokoergichesky connections (see).

G.'s metabolism proceeds through phosphate ethers and a nukleoziddifosfatsakhar, napr, through an uridindifosfatglyukoza (UDFG).

A constant source of G. in an organism is glycogen (see). At excess arrival of G. in a blood channel from a digestive tract under the influence of enzyme of a hexokinase (KF 2. 7. 1. 1) it turns into glyukozo-6-phosphate, from to-rogo glyukozo-1-phosphate is formed; the last turns into UDFG giving a glucose unit on synthesis of a glycogen.

Along with receipt from food and G.'s education from a glycogen in an organism there is also its synthesis, in particular from connections with shorter carbon chains, usually through their phosphate ethers. G.'s disintegration in an organism goes way glycolysis (see) or a pentozofosfatny way (see. Carbohydrate metabolism ).

In G.'s organism is an initial product for biosynthesis of some other sugars, napr, fructose, galactoses, xyloses, aminosugars, glucuronic to - you and other connections. Contents it in blood is supported by regulatory systems of carbohydrate metabolism on quite fixed level of 50 — 95 mg of % (by Gorodetsky's method). In blood take part in regulation of concentration of glucose as c. N of page, and hormones (insulin, glucagon, adrenaline, glucocorticoids, thyroxine, etc.). Decrease in contents of * in blood lower than 50 mg of % causes the sharp disturbance of activity of c, N of page which is observed sometimes at administration of insulin — so-called insulin shock. Distinguish a hypoglycemia of hepatic type (fiziol, a hypoglycemia of newborns; a hypoglycemia, the parenchyma of a liver coming at poisonings, infections, damages, squeezing of hepatic veins, at hunger and malnutrition, disturbance of a resorption of carbohydrates in intestines, at reduction of release of somatotropic hormone, adrenaline, glycocorticoids, thyroxine; so-called. infantile idiopathic hypoglycemia, hypoglycemia at glycogenoses I, III, IV, V and VI types, at a glikogennedostatochny disease, at a galactosemia, inborn sensitivity to fructose, at an idiopathic hyperlipemia), a hypoglycemia at the strengthened G.'s disintegration in fabrics (tumors of islets of Langerhans, a hyperplasia and a hypertrophy of islets of Langerhans, a passing hyper dysinsulinism, muscular tension, cooling, uraemic states, patol, sensitivity to proteins at the newborns born from mothers sick with diabetes) and, at last, a hypoglycemia at the strengthened G.'s allocation (disturbance of a resorption of G. in kidneys). Permanent increase in maintenance of G. in blood (see. Hyperglycemia ), the emergence which is not connected with meal, c it in urine (see. Glucosuria ) it is observed at a row patol, states. A hyperglycemia by origin share on insulyarny (at diabetes, bronze diabetes, Mauriac's syndrome, at an acute necrosis of a pancreas, acute pancreatitis, a pancreatic lithiasis, pancreatic cirrhoses and at fibroses of a pancreas) and ekstrainsulyarny: the alimentary, arising with participation c. N of page, at hypersecretion of a number of hormones, at various hepatopathies. At diabetes the strong hyperglycemia and a glucosuria are the most important symptoms of a disease. G.'s maintenance in urine of diabetics reaches 12%.

It is necessary for complete combustion of fats. G.'s lack leads to excess education fat to - t that leads to acidosis and a ketosis. Acidosis can result and from starvation since G.'s lack complicates use of own fats of an organism. In such cases intravenous or hypodermic administration of G. for elimination of acidosis is recommended.

Glucose as drug

(Clucosum; the synonym of Dextrosum) represents white fine-crystalline powder or inodorous colourless crystals, sweet taste, is well dissolved in water (1:1,5) and it is difficult in alcohol. It is possible to sterilize solutions G. 1 hour at 100 °, at more high temperature (119 — 121 °) — 5 — 7 min.

In medical practice use isotonic (4,5 — 5,0%) and hypertensive (10 — 40%) Solutions. The first are entered subcutaneously (from 300 ml and more kapelno), intravenously (kapelno), in enemas (300 — 2000 ml a day kapelno), the second — intravenously on 20 — 50 ml on one introduction, it is possible kapelno — to 300 ml a day.

G.'s introduction in isotonic solution leads to stimulation of functions of all cells of an organism since their energy balance improves. Drugs G. can be additional power supplies. The human body acquires on average in 60 min. apprx. 1 g of glucose (corresponds 1 d 5% of solution) for 1 kg of body weight.

Isotonic solution G. can be used also for replenishment of an organism by water at dehydration. Administration of hypertensive solutions G. leads to increase in osmotic pressure of blood, at the same time water and fabric substances direct from fabrics in blood, promoting dehydration of fabrics (the action opposite to effect of isotonic solution G.) and to removal of products of metabolism from them and substances alien to an organism. G.'s use as detoksikatsionny cure for poisonings with drugs, hydrocianic to - that and its salts, organic chemical matters (paints, etc.), by drugs of mercury and other metals is based on it.

Also stimulation of processes of metabolism, cardiotonic effect, vasodilatation, increase in a diuresis is a consequence of intravenous administration of hypertensive solutions G.

Hypertensive solutions G. are used for increase in volume of a liquid part of blood (e.g., at its condensation in case of extensive burns). At introduction to 10 — 40% solutions G. holds significant amounts of liquid.

Multilateral action and small toxicity of G. do it by high-valuable drug at diseases of a liver (dystrophy and a hepatatrophia, hepatitises, etc.), toxicoinfections, different intoxications, infectious diseases, disturbances of cordial activities (decompensations), hypostases. Also other means at their intravenous administration can be used as a component in blood-substituting and antishock liquids, and also for cultivation cordial (strophanthin, etc.).

The combination of 40% of solution G. from 5% is applied by solution of ascorbas of magnesium (drug «Magnesium ascorbas») at disturbances of cerebral circulation, frustration of a dream, vegetative neurosises. The combination of 25% of solution G. to 1% methylene blue is recommended by solution at a poisoning with cyanides.

As drug is produced in powders, tablets, in ampoules of various capacity (5 — 40% solutions).


Bibliography Kochetkov N. K. and d river. Chemistry of carbohydrates, M., 1967; M and l of e r G. R. and Kordes Yu. G. Fundamentals of biological chemistry, the lane with English, M., 1970, bibliogr.; Stepanenko B. N. Carbohydrates, Progress in studying of a structure and metabolism, it is gray. Results of science, M., 1968.

B. N. Stepanenko, V. K. Gorodetsky; G. V. Kovalyov (pharm.).

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