LETSITINA (synonym: phosphatidylsincalines, cholinephosphatides) — esters of amino alcohol of sincaline and diglitseridfosforny (fosfatidny) acids, are the most important representatives of phospholipids, in an animal organism carry out both structural, and metabolic functions, are a part of cellular membranes where their contents together with other phospholipids and cholesterol reaches 40%. In cellular membranes of L. form phospholipidic bisly, in Krom unpolar fat and acid «tails» of L. polar «heads» — outside are directed in a layer, and; they carry out interaction phospholipidic bisloya with a proteinaceous component of membranes. In cellular membranes of L., as well as other phospholipids (see. Phosphatides ), provide their selective permeability, serve Wednesday for transport of electrons, participate in activation of a large number of membrane enzymes. L. together with kephalins (see) are a part of myelin covers of nervous cells and fibers. Disturbance of exchange of L. in a human body leads to development of a number of diseases, including hereditary.
All natural L. are alpha letsitinami, i.e. contain the rest of phosphosincaline at alpha and carbon atom of glycerin:
L. differ from each other in the nature being their part fatty acids (see).
The prevailing number of natural L. contain at alpha and carbon atom the rest saturated fat to - you (hl. obr. palmitic or stearin), and in beta situation — the rest unsaturated fat to - you (olein, linolenic, etc.).
Pier. weight (weight) of L. fluctuates from 750 to 870 depending on being their part fat to - t. L., allocated from natural sources, represent white waxy matters, well soluble in organic solvents, except for acetone. Last feature of L. it is used for their separation and other phospholipids from cholesterol and triglycerides (neutral fats). The allocated L. usually represent mix of individual H.p. various zhirnokislotny structure therefore their t°pl is in limits 230 — 250 °, i.e. it is stretched. On air L. quickly turn yellow, and then darken owing to oxidation of the rest unsaturated fat to - you. L. solutions, in to - ry are very hygroscopic and form with water particles of L. are in a form of micelles. At neutral reaction of the environment and fiziol, pH values of L. exist in the form of zwitter-ions (bipolar ions). At alkaline or acid hydrolysis molecule L. breaks up to two molecules fat to - you and to molecules of glycerin, phosphoric to - you and sincaline.
L. are eurysynusic. They meet in animal, vegetable fabrics and in microorganisms. Their keeping in bodies and tissues of animals with high metabolic rate — in a liver, a cardiac muscle, nervous tissue, and also in quickly sharing cells is especially big. L are rich. egg yolks, fish roe, beans of soy.
L. lipoproteids of all classes participate in formation of the phospholipidic monolayer surrounded with an outside fibrous casing as provides solubility of lipoproteids in water. L are richest. lipoproteids of high density, or alpha lipoproteids, in to-rykh the maintenance of L. and other phospholipids are reached by 25%. L. lipoproteids of high density participate in the etherification of cholesterol catalyzed by enzyme lecithin — cholesterol-acyltransferase (LHAT). LHAT-reaction is resulted by transfer of the rest unsaturated fat to - you from beta situation in a molecule L. on hydroxylic group of cholesterol and formation of its ether:
lecithin + cholesterol — >(LHAT) —> ether of cholesterol + lysolecithin.
The ether of cholesterol formed on a surface of a lipoproteidny particle migrates in a particle, and lysolecithin communicates albumine of blood. Due to LHAT-reaction the main part of ethers of cholesterol of a blood plasma is formed.
The hereditary autosomal and recessive disease is known, to-rogo repression of synthesis of JT of HUTS is the cornerstone. It is so-called family LHAT-insufficiency. At patients concentration of L is sharply increased. and not esterified cholesterol in blood and at the same time concentration of esterified cholesterol is considerably reduced. Hypochromia anemia owing to destruction of erythrocytes because of accumulation in them of cholesterol and L is characteristic of this disease., and also the renal failure developing as a result of adjournment of membranes of erythrocytes in renal tubules.
The role of L is peculiar. in membranes of air cells where they by way of exception contain in the molecule two rests saturated palmitic to - you and therefore are less sensitive to oxidation under the influence of oxygen of inhaled air. Dipalmitil-letsitin, being effective poverkhnostnoaktivny substance, prevents adhesion of inner surfaces of air cells and by that provides normal course of process of breath in lungs (see. Surfactant ).
In an animal organism there is both a disintegration, and biosynthesis of L. (see the scheme).
L. can be formed also as a result of enzymatic methylation of phosphatidylethanolamines or acylation of the corresponding lysolecithins. Biosynthesis of L. most actively proceeds in a liver and a wall of a small bowel, more slowly — in kidneys, skeletal muscles and especially in a brain.
Splitting of L. occurs at effect of enzymes lecithinases (see), consistently chipping off from molecules L. the remains fat to - t, sincaline or phosphosincaline.
At insufficient synthesis of L. in a liver use of triglycerides and cholesterol for education is broken lipoproteids (see) that leads to accumulation of these lipids in a liver and development of her fatty dystrophy. In such cases use is shown lipotropic substances (see), including and letsitin.
In a blood plasma of the person from total quantity of phospholipids (on average 200 mg of %) apprx. 60 — 70% falls to the share of L. Increase in maintenance of L. in blood (lecithinemia) it is usually observed against the background of increase in concentration of all phospholipids and occurs at patients with a diabetes mellitus, hypothyroidism, glomerulonephritis, nephrosis, various diseases of a liver, especially biliary cirrhosis. Moderate decrease in maintenance of L. in a blood plasma in comparison with normal amounts it is observed at severe forms of an acute hepatitis, portal cirrhosis and at fatty dystrophy of a liver.
In laboratory a wedge, practice often define the so-called letsitinkholesterinovy coefficient representing the relation of content of the general phospholipids (but not one L.) to concentration of cholesterol. Normal this coefficient is quite constant. Its size fluctuates ranging from 1 to 1,5, but at a number of diseases, e.g. at atherosclerosis, decreases below unit.
Maintenance of L. determine by various hromatografichesky methods.
Letsitina as pharmaceuticals apply at a number of diseases of a nervous system, an adynamy, anemia, hypotonia, overfatigue, etc. In to lay down. to practice use tserebroletsitin (Cerebrolecithinum), received from a brain of cattle. Produce tserebroletsitin in tablets, coated, 0,05 g (in packaging on 40 pieces). Appoint 3 — 6 tablets a day.
Store in the dry, protected from light place at a temperature not over 20 °.
In the form of tablets produce also the lecithin cleared (Lecithinum purificatum) received from lecithin of soy crude food. The lecithin purified represents homogeneous mass from mazeobrazny to more dense consistence, yellow or yellow-brown color, with a peculiar smell and taste. On air under the influence of light darkens.
See also Antikholesterinemichesky means .
Bibliography: Alimova E. K., Astvatsaturyan A. T. and Zharov L. V. Lipids and fatty acids are normal also at a number of morbid conditions, M., 1975; Mosquitoes F. I., Korovkin B. F. and Menshikov V. V. Biochemical researches in clinic, L., 1976; Lipids, Structure, biosynthesis, transformations and functions, under the editorship of S.E. Severin, M., 1977; Mashkovsky M. D-Pharmaceuticals, p. 2, page 87, M., 1977; Lipids and lipidoses, ed. by G. Schettler, B., 1967; Phosphatidylcholine: biochemical and clinical aspects of essential phospholipids, ed. by H. Peeters, B., 1976; Phospho-lipide in biochemie, ed. by G. Schettler, Stuttgart, 1972.
A. H. Klimov; A. I. Tentsova (pharm.).