DECARBOXYLATION

From Big Medical Encyclopedia

DECARBOXYLATION — process of eliminating of carbon dioxide (CO 2 ) from organic acids or amino acids. In biol, systems essential value — biochemical and physiological — has D. of amino acids and ketonic acids. D.'s reaction can make a part of the general mechanism of transformation of amino acids therefore the biogenic amines having high pharmacological activity are formed.

Of amino acids is one of the main ways of an intermediate metabolism of amino acids at all organisms. Depending on the chemical nature of amino acid as a result of D. biogenic are formed amines (see) or new beta, and gamma and monocarboxylic amino acids. D.'s reactions are catalyzed by specific enzymes — decarboxylases (see) also proceed according to the following scheme:

Only L-stereoizomery of amino acids are exposed to enzymatic D.; the exception is made by a meso-alpha, an epsilon - diaminopimelic to - that, in a cut two stereoisomeric carbon atoms contain, one is in L-, and another in a D-configuration. In an organism there can be coupled reactions of D. and interaminations (see) or D.'s reactions and deaminations (see) a lysine, arginine and their derivatives. So, the enzyme catalyzing oxidizing transformation of a L-lysine to delta and aminovalerian to - you, by CO is found in bacteria of Pseudomonas 2 and NH 3  :

D.'s reaction amino acids in animal fabrics is not quantitatively prevailing exchange reaction of amino acids what rather low activity of decarboxylases in their fabrics testifies to and rather small amount of substrates for D. Odnako D.'s products have big fiziol, value, biogenic amines, e.g., are physiologically active even in very low concentrations. For the first time K. M. Rozanov in 1936 showed formation of a histamine in animal fabrics by D. of a histidine. In tissues of animals intensively proceeds. dioxyphenylalanine (see) with formation of dopamine (oxytyramine) which is, on modern representations, a predecessor of noradrenaline and adrenaline in an organism of animals. The histamine lowers the blood pressure, and tyramine, triptamin and especially 5-oksitriptamin (serotonin) possess hypertensive action. High pharmakol. some derivatives of these amines have activity (adrenaline, noradrenaline, ephedrine, sincaline, etc.). The sequence of data demonstrates increase in blood pressure at disturbance of blood circulation in kidneys (ischemia, etc.) in connection with accumulation in renal fabric of amines for which oxidation oxygen is necessary. It is supposed that some disorders of mental activity are caused by intoxication of an organism the biogenic amines formed in fabrics. Thus, D.'s processes amino acids in an organism, perhaps, participate in regulation of some fiziol, processes. Besides, D.'s products of amino acids — taurine, beta alanine and others are necessary for biosynthesis of a number of the difficult connections which are carrying out specific biol, functions. The equations of the most widespread reactions of D. of amino acids and their derivatives are given in an organism of animals and the person below.

In animal fabrics availability of the enzyme of a decarboxylase of aromatic L-amino acids (KF 4.1.1.28) catalyzing D. of almost all aromatic amino acids is proved.

Orthotyrosine, metatyrosine and alpha and methylderivatives of tryptophane, tyrosine and DOFA are also decarboxylized by this enzyme. Fermental drugs from a medulla of adrenal glands and kidneys of rats do not catalyze, however, D. tryptophane and tyrosine, but decarboxylize DOFA. The special enzyme catalyzing, apparently, D. of a histidine is found in mast cells. There are data that tryptophane is decarboxylized by fermental drugs from kidneys only after its oxidation to 5 oxytryptophanes and that 5 oxytryptophane are substrate for D., as a result to-rogo is formed physiologically active 5-oksitriptamin (serotonin).

Big fiziol. value for the person and animals has D .L - glutamino-howl to - you (see. Glutamic acid ). Opening piperidic to - you (GAMK) followed detection in homogenates of a brain of L - glutamatdekar-boksilazy (KF 4.1.1.15), the catalyzing D. of a L-glutamate with formation of piperidic acid.

The weight of evidence suggests that GAMK is among transmitters of nervous impulses. Besides, GAMK can pereaminirovatsya with pyroracemic, alpha and keto-glutaric and, perhaps, some other ketonic acids with formation of the corresponding amino acid and semi-aldehyde amber to - you; oxidation of the last to amber to - you provide functioning of a bypass way of oxidation L-glutami-new to - you, passing alpha and keto-glutaric to - that. On the scheme interface of two ways of oxidation of L is shown - glutamino-howl to - you with a cycle Tricarboxylic to - t (see. Tricarboxylic acids cycle ).

For mitochondrions of a brain L-glutaminic to - that, but not glucose is the main substrate of breath. In this regard a bypass way of transformation L-glutaminic to - you with participation of a glutamatdekarboksilaza get big fiziol, value. According to V. L. Kretovich (1972) data obtained on the higher plants, regulation of system glutaminic to - that GAMK + CO 2 the essential role in the general process of regulation of contents in a cell glutaminic to - you and the glutamine which is mother substance for biosynthesis of many the connections, vital for a vegetable organism, belongs. It is probable that the same role of D. L-glutaminic to - you play in an organism of animals and the person.

D.'s process is eurysynusic at microorganisms. During the rotting of proteins formation of amines is caused by D. of various amino acids under the influence of bacterial decarboxylases (see. Rotting ).

In a research D. of amino acids the Soviet researchers achieved considerable achievements from microorganisms. S. R. Mardashev in 1947 from cells of a bacterium of Pseudomycobacterium n. sp. allocated the specific decarboxylase which is chipping off CO 2 from beta COOH - group L-asparaginic to - you with formation of a-alanine. In 1950 in the same laboratory the type of Micrococcus of the item sp was allocated., containing the decarboxylase specific concerning a L-histidine. Using these bacteria, S. R. Mardashev with sotr. developed a bystry and exact method of definition asparaginic to - you and a histidine in proteins. L-asparaginic to - you are unique reaction as at the same time it is decarboxylized beta-SOON-, but not alpha COOH - group as it usually occurs at D. of amino acids.

Fermental drugs aspartate - beta decarboxylases (aspartate-1-dekar-boksilazy; KF 4.1.1.11) were received from a number of microorganisms, including and from Achromobacter; in the latter case enzyme was received in crystalline state. This enzyme is activated not only piridoksal-5 '-phosphate that is characteristic of decarboxylases of amino acids, but also catalytic amounts of alpha ketonic acids.

D.'s reactions amino acids are eurysynusic also at the higher green plants. It is important to note that D.'s reactions at plants have a direct bearing on biosynthesis of a number of alkaloids.

S. R. Mardashev and it sotr. it was established that urocanic to - that is inhibitor of a histidinedecarboxylase (KF 4.1.1.22). Since contents urocanic to - you in skin of patients at some dermatosis is lowered, it was possible to expect in this case more active D. of a histidine with formation of the histamine promoting a dermatosis.

The attempt of use to lay down was made. the ointments containing urocanic to - that, for therapy of a dermatosis; tentative data demonstrate positive effect.

Piperidic to - that is D.'s product of a L-glutamate — is applied to treatment patol, the states connected with disturbance of functions of c. N of page: during the easing of memory, atherosclerosis of brain vessels and disturbances of cerebral circulation, after the postponed injuries and paralyzes, at a headache, sleeplessness, dizzinesses connected with an idiopathic hypertensia in pediatrics — at mental retardation.

Of ketonic acids it was for the first time revealed To. Neyberg in 1911. In beer yeast extracts it found the specific enzymes catalyzing D. pyroracemic, alpha-oxobutyric, alpha and ketovalerian and other a-ketonic acids with formation of the corresponding aldehyde and CO 2 . D.'s reaction ketonic acids proceeds according to the scheme:

Later D.'s existence alpha and keto-glutaric to - you was proved. From extracts of the higher plants specific decarboxylases alpha and keto-glutaric and oxalacetic to - t were allocated. It was shown that D. oxalacetic to - you (oxalate) with education pyroracemic to - you (pyruvate) is carried out by the p-decarboxylase attacking beta COOH - group that distinguishes it from Neyberg's alpha decarboxylase.

In tissues of animals of alpha ketonic acid are exposed to oxidizing D. with education corresponding shortened on one carbon atom carboxylic to - t and CO 2 . In the course of fabric exchange of carbohydrates, fats and proteins as intermediate products also others are formed Pyroracemic, alpha and keto-glutaric, oxalacetic and - ketonic acids. Accumulation can lead them (especially pyroracemic to - you, formed also as a result of other metabolic transformations) to disturbance fiziol, functions, and first of all — functions of c. N of page. As all decarboxylases of a-ketonic acids are complex enzymes which coenzyme is the fosforilirovanny form of vitamin B 1 — thiamine pyrophosphate, at B1 avitaminosis disturbances of functions of a nervous system, napr take place, at a polyneuritis.

Pyroracemic to - you many works are devoted to clarification of ways of oxidation. In 1943 Krebs offered the scheme of transformation pyroracemic to - you through a cycle of di - and tricarboxylic to - t (see. Tricarboxylic acids cycle ), in Krom one molecule pyroracemic to - you are oxidized with formation of three molecules CO 2 and two molecules H 2 O (see. biological oxidation ). Details of the mechanism of this reaction and a way of its regulation are found out. In the main way of transformation pyroracemic to - you in animal fabrics, at plants and at aerobic microorganisms are its oxidizing D. to atsetil-KOA, catalyzed by a multifermental piruvatdegidrogenazny complex. Alpha and keto-glutaric to - you is also carried out with the participation of similar alpha ketoglutaratdegidrogenaznogo a complex.

The full oxidation of alpha ketonic acids beginning with oxidizing D. to CO 2 and H2O promotes energy release, life activity, necessary for course of processes, in any live organisms, and a considerable part of this energy collects in vysokoergichesky pyrophosphatic bonds of ATP.

See also Nitrogen metabolism , Amino acids .



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T. T. Berezov, 3. S. Kagan.

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