CITRIC ACID (2 - hydroxy - 1,2,3 - propane tricarboxylic acid, beta hydroxytricarballylic acid; Acidum citricum) — aliphatic tricarboxylic oxyacid. Formula of citric acid:
L. to. is a key link of the major recycling of the higher organisms (eukaryotes) — a cycle of Tricarboxylic acids, realizing the power mechanism of a cell. L. to. participates in regulation of biosynthesis of the highest fat to - t, exchange of carbohydrates and in regulation of other processes as an allosteric effector of the corresponding enzymes, it is a source of education acetyl - and tsitrilfosfat. L. to. also important role in exchange of calcium belongs. Salts L. to. (citrates) and she are widely applied in a lab. and wedge, researches of disbolism and various fiziol, states; anti-ketogenic effect of sodium citrate and excitement of a number of reflexes by it is noted, in particular. Determination of content of L. to. in blood it is used in diagnosis of cardiovascular and endocrine diseases, rickets, etc. Complex salts L. to., marked 67 Ga and 111 In, apply to radio isotope diagnosis of tumors. Natrii citras pro injectionibus, connecting a part of calcium of blood serum, in a nek-swarm of degree promotes the prevention of thromboses that is used at a myocardial infarction, stenocardia and heart attacks of a brain. Tsitratoterapiya is applied to a litoliz of urinary stones. L. to. (in combination with vitamin D) it is effective at treatment of rickets. Sodium citrate and L. to. widely use as anticoagulants during the receiving stored blood and a blood plasma. Anticoagulative effect of citrate is based on transition of the calcium which is contained in blood to calcium citrate that causes in turn transition of a prothrombin to thrombin since the quantity of ions of Ca2+ activating thromboplastin sharply decreases.
Ranges of application of L. to. are very various. It is widely used in the food industry (as flavoring additive), at production pharm. drugs (an acid component), in cosmetics, galvanotechnics, in tanning production, in the photo and for other purposes. Trialkilovy ethers L. to. apply as plasticizers during the receiving products from plastic.
L. to. it is very eurysynusic in wildlife. As universal metabolite of L. to. contains in living cells of all higher organisms. More than 80% of all of L. to., contained in a human body and the highest animals, it is the share of the mineralized fabrics (a bone tissue, teeth, etc.). Maintenance of L. to. in blood of the person normal makes 2 — 3 mg of %; L. to. — constant component of urine.
In rather large numbers of L. to. collects in nek-ry plants (fruits of a citrus, berries of currant, a cranberry, root crops of beet, etc.); juice of unripe lemons contains 6 — 8% of L. to.
L. to. in usual conditions is one-water crystalline hydrate, represents transparent colourless crystals. L. to. shows complexing properties thanks to what forms well soluble and a little ionized complexes with ions of metals, napr, with calcium; it is of great importance for calcic exchange in an organism.
In the industrial way of receiving L. to. fermentation of sucrose or glucose (in the USSR — beet treacle) is special strains of a mold mushroom of Aspergillus niger.
In the absence of the disturbing substances L. to. determine by titration by alkali or (including salts L. to.) by methods of oxidimetry (permanganato-or a vanadatometriya), and also photometry (in the form of complexes L. to. with copper and iron). For quantitative determination
of L. to. in biol, materials the method based on its transformation in pentabromatseton is widely applied, to-ry in the form of connection with thiourea define quantitatively spektrofotometrichesk or photometric; use also a flyuorimetriya (e.g., a flyuorimetriya of reaction product L. to. with acetic anhydride and pyridine), an electrophoresis and other methods. For definition of surplus citrate-anions in a citrated blood use the principle of recalcification (finding of the minimum quantity of the calcium causing coagulation of a sample of a citrated blood).
Participating in the major recycling (see. Tricarboxylic acids cycle ), L. to. it is synthesized by condensation atsetil-KOA with oxalacetic to - that and isomerized (through cis-aconitic to - that) in isolemon to - that (1-hydroxy-1, 2, 3-propane tricarboxylic to - that), edges and undergoes further splitting. Similar role of L. to. carries out in the glioksilatny cycle characteristic of microorganisms and plants.
Bibliography: Afanasyev V. G., Zaytsev V. S. and Wolfson T. I. To a micromethod of definition of citric acid in blood serum by means of the photoelectrocolorimeter, Laborat, business, No. 2, page 115, 1973: Babble y M. F. About zv'yazok tricarboxylic to a cycle z deyaky processes about-mshu rechovin, the Uke. 6ioxiM. zhurn., t. 42, No. 2, page 175, 1970, bibliogr.; Lenin-dzher A. Biochemistry, the lane with English, M., 1976; H e of N and c of e with to at K. D. Organic chemistry, the lane from Romanians., t. 2, page 118, M., 1963; H and of t 1 e s R. L. Citrate in mineralized tissues, Advanc, oral Biol., v. 1, p. 225, '1964.
A. I. Tochilkin.