CARBOXYLATION — addition reaction to organic matters of CO carbon dioxide 2 with formation of a carboxyl group — COOH; occupies one of the central places in a metabolism and circulation of carbon in the biosphere. Opposite process carries the name decarboxylations (see). As a rule, reactions To. demand energy consumption and therefore in live organisms are accompanied by reaction of hydrolysis of ATP or others vysokoergichesky connections (see). The enzymes catalyzing To., are called carboxymanholes.
Carboxymanholes are eurysynusic in wildlife, they are found in plants, microorganisms and animals. All carboxymanholes contain covalent and connected biotin (see) which is exposed to a carboxylation carbonic acid (more precisely HCO bicarbonate ion 3 - ), turning into carboxybiotin; at this stage the energy which is marked out at hydrolysis of ATP is used. Then there is a transfer of COOH group from carboxybiotin on the second substrate of enzyme. At a lack of biotin (avitaminosis of N) of reaction To. in an organism are broken that affects first of all the exchange processes proceeding in skin.
Reaction To. pyroracemic to - you (pyruvate) with education oxalacetic to - you (oxaloacetate) are catalyzed piruvatkarboksilazy (pyruvate: CO 2 - ligase; KF 126.96.36.199) is also the first stage of a gluconeogenesis, i.e. synthesis of glucose from pyroracemic to - you. For the account To. pyruvate there is also a replenishment of fund of the oxaloacetate necessary for functioning of a cycle Tricarboxylic to - t (see. Tricarboxylic acids cycle ); this way there can be a fixing of carbon of carbonic acid in strukturnofunktsionalny components of a cell in the course of use of substances of a cycle Tricarboxylic to - t for synthesis of amino acids, gem, etc.
Atsetil-KOA — a carboxymanhole (malonil-KOA — a sintetaza; KF 188.8.131.52) catalyzes transformation of the rest acetic to - you, connected with KOA, in the rest low-new to - you. Formed at the same time malonil-KOA is a source of the majority of carbon atoms fat to - t in the course of their biosynthesis; The COOH group of the rest low-new to - you in this process is chipped off and, therefore, carbon of carbonic acid in fat to - you does not get.
The Propionil-Koa — a carboxymanhole (KF 184.108.40.206) catalyzes transformation of the rest propionic to - you, connected with KOA, in the rest methyl-malonic to - you. This reaction is similar to previous.
Some reactions To. at plants and other autotrophic organisms have much wider value: they form the main way through which the flow of carbon of atmospheric carbonic acid goes to organic matters of autotrophic organisms and the biosphere in general. In process photosynthesis (see) at plants serves as such reaction To. ribulozo-1,5-diphosphate with formation of two molecules phosphoglyceric to - you. Enzyme of a ribulozodifosfatkarboksilaz (ribulozodifosfatkarboksidismutaz; KF 220.127.116.11) in large numbers contains in chlorolayers of plants.
At a number of plants and photosynthesizing bacteria fixing of CO 2 it is carried out in the way To. the fosfoyenolpiruvata with formation of oxaloacetate is also catalyzed by fosfoyenolpiruvatkarboksilazy (KF 18.104.22.168).
In a wedge, practice definition of activity of the enzymes catalyzing reactions To. in fabrics and biological liquids, it is not made yet.
See also Metabolism and energy .
Bibliography: Kondratyeva E. H. Photosynthesizing bacteria, M., 1963, bibliogr.; Lenindzher A. Biochemistry, the lane with English, page 112, M., 1974; P at - B. A. and Gavrilenko's bin of V. F. Biokhimiya and physiology of photosynthesis, M., 1977; M about s s J. Lane M. D. Biotin-dependent enzymes, Advanc. Enzymol., v. 35, p. 321, 1971, bibliogr.
A. Ya. Nikolaev.