VITAMINS

From Big Medical Encyclopedia

VITAMINS (Latin vita life + amine[s]) — the feedstuffs necessary for maintenance of vital signs. On a structure are low-molecular weight compounds of various chemical nature. The human body and animals is not synthesized by V. or synthesizes in insufficient quantity and therefore shall receive them in finished form. It are required for an organism from several micrograms to several milligrams a day century (see the tab.). Unlike other irreplaceable factors of food (irreplaceable amino acids, unsaturated fatty acids, etc.), V. are not plastic material or an energy source and participate in a metabolism preferential not as substrates biochemical, reactions and as participants of mechanisms of a biocatalysis and regulation separate biochemical, and fiziol, processes.

V.'s lack of food or change of processes of their assimilation leads to disbolism and eventually to development hypo - and avitaminosis (see. Vitamin deficiency ).

V.'s opening is closely connected with studying of a role of separate feedstuffs in ensuring good nutrition. In the second half of 19 century was considered that for normal functioning of an organism of rather certain contents in food of proteins, fats, carbohydrates, mineral salts and waters.

In 1880 the Russian researcher N. I. Lunin established that in foodstuff there are still unknown factors of food necessary for life. It showed that the white mice receiving whole milk grew well and were healthy, but perished when they were fed with mix from the main components of milk: casein, fat, lactose, salts and water. N. I. Lunin's conclusions were confirmed further by S. A. Sosin (1891), and in 1906 — 1912 F. Gopkins.

In 1897 goal. doctor Eykman (Ch. Eijkman) established that at the hens receiving the polished rice in food the disease, similar to beriberi, developed, however they recovered after they were given rice bran.

According to the proposal of the Polish scientific K. Funk (1911 — 1912) who was working on allocation of the active beginning of rice bran and found existence in them of an amino group, all substances of this sort began to call vitamins («vital amines»).

It is known about two tens substances which can be carried to V. Prinyato to distinguish water-soluble and fat-soluble V. K the first belong ascorbic to - that (redoxon), and also vitamins of group B.: thiamin (vitamin B 1 ), Riboflavinum (polyneuramin 2 ), pyridoxine (vitamin B 6 ), cobalamines (vitamin B 12 ), Niacinum (PP vitamin, nicotinic to - that), Folacinum (folic to - that), pantothenic to - that and biotin. Carry Retinolum (vitamin A), calciferols (vitamin D), tokoferola (vitamin E) and phylloquinones (phthiocol) to fat-soluble V. Along with V. which need for the person and animals is undoubtedly established and deficit leads to the phenomena of a vitamin deficiency, there are also other biologically active agents which functions have not so specific character. These substances can be ranked as vitaminopodobny connections. Usually carry bioflavonoids, sincaline, an inositol, lipoic, orotovy, pangamovy and paraaminobenzoic acids to them. Paraaminobenzoic to - that is a growth factor for some microorganisms synthesizing from it folic to - that. For the person and animals paraaminobenzoic to - that is biologically inactive since they are not capable to turn it in folic to - that.

A number of V. is presented not by one, but several connections possessing similar biol, activity. The group of B6 vitamin including a pyridoxine, piridoksal and pyridoxamine can be an example. For designation of similar groups of related connections according to recommendations of the International union of specialists in food (1969) alphabetic references are used (A, D vitamins, etc.). For designation of the individual connections having vitamin activity it is recommended to give the rational names reflecting their chemical essence, napr, a retinal (an aldehydic form of vitamin A), ergocalciferol and cholecalciferol (a form of vitamin D). The chemical structure of famous V. is completely established, most of them is received by chemical synthesis. Chemical, and also mikrobiol, synthesis is a basis of modern industrial production of the majority

to V. Kroma V., provitamins — connections which, without being vitamins, can serve as predecessors of their education in an organism are known. The karotina which are split in an organism with formation of Retinolum (vitamin A), some sterols (ergosterol, 7 Dehydrocholum sterol, etc.) turning into vitamin D concern to them.

Some derivative V. with the replaced functional groups render action, opposite in comparison with V., on an organism, i.e. are antivitamins. Getting into cells, these substances enter the competitive relations with V., in particular at biosynthesis of coenzymes and formation of active enzymes. Having taken V.'s place in structure of enzyme, antivitamins owing to distinctions in a structure cannot perform their functions. Carry to antivitamins also the substances connecting or destroying V. (see. Avidin , Thiaminase ). A number of antivitamins has antimicrobic activity and is applied as chemotherapeutic means as, e.g., sulfanamide drugs.

Specific function of vitamins of group B in an organism consists that are formed of them coenzymes (see) and the prosthetic groups of enzymes which are carrying out many major exchange reactions of substances. So, thiamin (polyneuramin 1 ) turns in an organism into the thiamin-diphosphate (cocarboxylase) which is a coenzyme of the euzymatic systems which are carrying out oxidizing decarboxylation of α-ketonic acids..........

The enzymes connected with various V. take part in implementation of many major processes of a metabolism: energy balance (oryzamins and B2), biosynthesis and transformations of amino acids (B6 and B12 vitamins), fatty acids (pantothenic to - that), the purine and pirimidinovy bases (folic to - that), formation of many physiologically important connections (acetylcholine, steroids), etc. Coenzymes and prosthetic groups and furthermore the corresponding V., in itself have no catalytic activity and get it only at interaction with specific proteins — apoenzymes.

V.'s introduction, including in the raised doses, cannot normalize the speed of the related biochemical reaction if it is lowered not because of this V.'s lack, and owing to any other disturbances. From this point of view V.'s use in medical practice in the dosages considerably exceeding fiziol, requirement, can be not always justified, and in some cases and is unsafe as it can lead to disbolism and hypervitaminoses (see).

Unlike vitamins of group B, fat-soluble vitamins Retinolum, calciferols, tokoferola and phylloquinones, and also ascorbic to - that are not predecessors of coenzymes or prosthetic groups. These V.' functions are various and connected with implementation of processes of photoreception (vitamin A), blood coagulations (phthiocol), absorptions of calcium (vitamin D).

Necessary condition of implementation of specific functions B. in a metabolism is normal implementation of their own exchange: absorptions in intestines, transport in fabrics, turning into active forms. Absorption and V.'s transfer by blood are carried out, as a rule, by means of special transport proteins (retinosvyazyvayushchy protein for Retinolum, transcobalamines I and II for B12 vitamin etc.). Turning into. in active forms, in particular in coenzymes and prosthetic groups, and also joining of these prosthetic groups to apoenzymes are carried out by means of specific enzymes. So, the pyridoxal kinase catalyzes transformation piridoksalya (one of forms of B6 vitamin) in its coenzymatical form — pyridoxal phosphate. Tiaminpirofosfokinaza carries out transformation of thiamin in tiamindifosfat. Disturbance of one of these processes, e.g., at the inborn or acquired defect of biosynthesis of one of the specific proteins participating in this or that V.'s exchange makes impossible running in. the specific functions that leads to development of a partial or full vitamin deficiency. The anemia developing at inborn defect of absorption folic to - you in intestines can be an example of such disturbances or at genetic defect of the digidrofolatreduktaza turning folic to - that in its coenzymatical form — tetrahydrofolic to - that. Along with turning into active forms B. are exposed in an organism to catabolic transformations with formation of inactive forms in the form of which they can be brought from an organism (4-pyridoxynew to - that from a pyridoxine, N1-metilnikotinamid from nicotine of amide, etc.).

Insufficient arrival of V. in an organism or disturbance of their transformation can be defined by a research of the vitamin status of the person. For this purpose define V.'s maintenance and products of their exchange in blood, urine, activity of enzymes into which composition in the form of a coenzyme or prosthetic group this V., and also others biochemical, and fiziol, the indicators characterizing specific functions B enters.

Methods of definition of vitamins are given in articles devoted to separate vitamins (e.g., Ascorbic acid, Retinolum, Thiamin, etc.). It is applied as well a tracer technique (see. Vitamin deficiency , radio isotope diagnosis).

By means of histochemical methods it is possible to reveal existence in fabrics of Retinolum, Riboflavinum and ascorbic to - you.

Definition ascorbic to - you is based on its property in the dark and in the cold to recover acid solutions of caustic silver. There are various modifications of methods based on processing by acid solutions of caustic silver of unstable fabric blocks or fresh frozen sections. Also the method of processing of freeze-dried sections is offered. However some researchers [J.F. Danielli, G. Kiszely, etc.] call into question specificity of methods in general in connection with ability of redoxon to diffusion and, perhaps, existence in fabrics of other strong reducers of silver. So, Klara (M. of Clara), though considers these methods suitable for identification ascorbic to - you, however point to property of granules of α-cells of islands of a pancreas, substance of enterokhromaffinny cells, an adrenokhrom, melanin, neurosecretory granules of supraoptic and paraventrikulyarny kernels of a hypothalamus also to recover acid solutions of silver.

Bourne's method enjoys the greatest popularity (G. N of Bourne) both A. Giroud method and Le Blond (Page P. Leblond).

The method to Fat and Le Blond allows to receive the thin paraffin sections convenient for studying. The fresh fabric block of 2x3x2 mm in size place for 30 — 40 min. in 10% solution of the caustic silver acidified concentrated acetic to - that to pH 3,0 — 4,0; then solution is merged and pieces of fabric wash out several times a distilled water and for 30 min. place solution of sodium hyposulphite then fabric blocks dehydrate alcohols of the ascending concentration in 6% and according to the usual scheme conclude in paraffin. All procedures, except for paraffin embedding, carry out in the dark. The received paraffin sections slightly tint mix of imperial green and pyronin. Sites of localization ascorbic to - you have an appearance of small black granules.

Definition of Riboflavinum is based on recovery by its hydrogen (at the time of education) to a leykoflavin who on air is oxidized to the rodoflavin having red color. Fabric is fixed formalin and carry out reaction on frozen sections. Cuts place for 30 min. in 1 — 2% salt brine to - you, in to-ruyu add zinc dust; then they are washed out in water and within several hours maintained in a Petri dish or on clock glass on air and concluded in glycerin-gelatin. Flavoproteins are painted in red color.

Identification of vitamin A is based on its property to give bright green fluorescence in ultraviolet rays with the wavelength of 365 nanometers. Fresh thin fabric blocks fix 10% solution of cold formalin no more than for 10 — 12 hour. Then immediately prepare frozen sections which study in water. The luminescence disappears in 10 — 60 sec. (it must be kept in mind that the resistant luminescence is caused not by vitamin A). For control cuts process solution salt to - you.

Separate vitamins — see articles according to the name of vitamins (e.g., Ascorbic acid , Calciferols , Niacin , Cyanocobalamine etc.).


The main properties, functions and indications to medical use of vitamins

Bibliography: Vitamins, under the editorship of M. I. Smirnov, M., 1974; Polyneuramins food and prevention of a vitamin deficiency, under the editorship of V. V Efremov, M., 1969, bibliogr.; Vitamins and vitamin drugs, under the editorship of V. A. Yakovlev, M., 1973; Hygiene of food, under the editorship of. K. S. Petrovsky, t. 1, page 88, M., 1971; Efremov V. V. Discovery of vitamins by N. I. Lunin, Vopr, food, t. 12, No. 5, page 3, 1954; P. E Kalmyks. and L ogatkin M. N. Modern ideas of a role of components of food, page 139, L., 1974; Molecular bases of pathology, under the editorship of V. N. Orekhovich, page 220, M., 1966, bibliogr.; Yurkevich A. M., Severin S. E. and Braunshteyna. E. Organic cofactors of enzymes — coenzymes, in book: Enzymes, under the editorship of. A. E. Braunshteyna, page 147, M., 1964, bibliogr.; Funk C. Die Vitamine, Miinchen — Wiesbaden, 1922; Lunin N. Uber die Bedeutung der anorganischen Salze fur die Ernahrung des Tieres, Diss., Dorpat, 1880; The vitamins, ed. by W. H. Sebrell a. R. S. Harris, v. 1—7, N. Y. — L., 1967 — 1972.

Histochemical methods of definition of V. in fabrics — Kissels D. Prakticheskaya of the microtechnician and a histochemistry, the lane with Wenger., page 188, etc., Budapest, 1962; Lille R. Patogistologicheskaya of the technician and a practical histochemistry, the lane with English, page 399, M., 1969; Pearce E. A histochemistry, the lane with English, page 244, etc., M., 1962; Ros-kin G. I.ilevinson L. B. Mikroskopicheskaya of the technician, page 276, M., 1957.

V. V. Efremov, V. B. Spirichev; R. A. Simakova (stalemate. An.).

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