Decarboxylation of amino-acids

1 a-Decarboxylation of Amino Acids If the electron-withdrawing effect of the heterocyclic nitrogen of pyridoxal phosphate is primarily centered on the a -carbon-carboxyl bond, the result is decarboxylation of the amino acid aldimine and release of CO2. The resultant carbanion is then protonated, and the primary amine corresponding to the amino acid is displaced by the lysine residue at the active site, with reformation of the internal Schiff base. 

A number of the products of the decarboxylation of amino acids shown in Table 9.2 are important as neurotransmitters and hormones, such as dopamine, noradrenaline, adrenaline, serotonin (5-hydroxytryptamine), histamine, and Y - aminobutyric acid (GABA), and as the diamines agmatine andput-rescine and the polyamines spermidine and spermine, which are involved in the regulation of DNA metabolism. The decarboxylation of phosphatidylser-ine to phosphatidylethanolamine is important in phospholipid metabolism (Section 14.2.1). 

Dopamlne (dlhydroxyphenylethylamine) DOPA (3,4-dihydroxyphenylalanine) Aromatic amino acid decarboxylase 4.1. 1.28 

Serotonin (5-hydroxytryptamine) 5-Hydroxytryptophan Aromatic amino acid 4.1.1.28 

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The first stage of the reaction is a special case of the oxidative decarboxylation of amino acids, for which two general mechanistic hypotheses are under discussion.This is followed by aromatiz-ation. A possible mechanism (241- 242- 243- 245) has been... 

Be Pyridoxine, pyridoxal, pyridoxamine Coenzyme in transamination and decarboxylation of amino acids and glycogen phosphorylase role in steroid hormone action Disorders of amino acid metabolism, convulsions... 

TABLE 4. Efficiency of decarboxylation of amino acids at pH 10.1 by hydroxy radicals... 

Decarboxylation of amino acids yields bioactive amines including CNS neurotransmitters. 

The catecholamines noradrenaline (norepinephrine) and adrenaline (epinephrine) are amines derived via decarboxylation of amino acids. Noradrenaline is a mammalian neurotransmitter, and adrenaline, the... 

Amine build-up in fish muscle usually results from decarboxylation of amino acids in the muscle by enzymes of bacterial origin. This review will present information on the activity of bacterial decarboxylases and the formation of amines in fish. Mechanisms of decarboxylase action and production of bacterial decarboxylases in fish muscle are discussed. Emphasis is placed upon studies dealing with formation of histidine decarboxylase and histamine. Histamine, because of its involvement in Scombroid food poisoning, has been extensively studied with regard to its formation in fish and fishery products. 

Histamine is synthesized in tissues by decarboxylation of amino acid L-histidine, a process catalyzed by the pyridoxalphosphate-dependent enzyme L-histidinedecarboxylase. Histamine can enter the organism with food it also can be generated by bacteria of the gastrointestinal tract. However, these sources do not create additional reserves of histamine since exogenous histamine is easily catabolized in the organism. 

Pyridoxal phosphate is the coenzyme for the enzymic processes of transamination, racemization and decarboxylation of amino-acids, and for several other processes, such as the dehydration of serine and the synthesis of tryptophan that involve amino-acids (Braunstein, 1960). Pyridoxal itself is one of the three active forms of vitamin B6 (Rosenberg, 1945), and its biochemistry was established by 1939, in considerable part by the work of A. E. Braunstein and coworkers in Moscow (Braunstein and Kritzmann, 1947a,b,c Konikova et al 1947). Further, the requirement for the coenzyme by many of the enzymes of amino-acid metabolism had been confirmed by 1945. In addition, at that time, E. E. Snell demonstrated a model reaction (1) for transamination between pyridoxal [1] and glutamic acid, work which certainly carried with it the implication of mechanism (Snell, 1945). 

A number of the reactions in which HOCl and O2 might participate to kill bacteria and to attack biological molecules have been documented. These include the halogenation of tyrosines, the formation of aldehydes and chloramines, the attack of Oj on unsaturated bonds in fatty acids, and decarboxylation of amino acids. The experimental basis for these reactions has been reviewed by Klebanoff and Clark... 

Both the ninhydrin reaction and pyridoxal phosphate-catalyzed decarboxylation of amino acids (Chapter 14) are examples of the Strecker degradation. Strecker reported in 1862 that alloxan causes the decarboxylation of alanine to acetaldehyde, C02, and ammonia.c... 

These also presumably lead to a transient quinonoid-carbanionic intermediate. Addition of a proton at the original site of decarboxylation followed by breakup of the Schiff base completes the sequence. Decarboxylation of amino acids is nearly irreversible and frequently appears as a final step in synthesis of amino compounds. For example, in the brain glutamic acid is decarboxy-lated to y-aminobutyric acid (Gaba),193 196b while 3,4-dihydroxyphenylalanine (dopa) and 5-hydroxy-... 

Receptors for histamine, which probably acts as a neuromodulator,801 occur in the brain.802 Histamine is formed by decarboxylation of histidine (p. 745)803 and is inactivated by histidine N-methyltransferase. Histamine is best known for its presence in mast cells,804 components of the immune system that release histamine during inflammatory and allergic reactions (Chapter 31). However, histaminergic neurons of the hypothalamus extend throughout the whole forebrain,805 and specific receptors have been found both in the brain and in peripheral tissues.806 Several other amines that are formed by decarboxylation of amino acids are present in trace amounts but may have im-... 

Pyridoxal phosphate enzymes mediate the nonoxidative decarboxylation of amino acids. This mechanism is of primary importance in bacteria, but it may be essential to proper function of the nervous system in humans... 

Several of the B vitamins function as coenzymes or as precursors of coenzymes some of these have been mentioned previously. Nicotinamide adenine dinucleotide (NAD) which, in conjunction with the enzyme alcohol dehydrogenase, oxidizes ethanol to ethanal (Section 15-6C), also is the oxidant in the citric acid cycle (Section 20-10B). The precursor to NAD is the B vitamin, niacin or nicotinic acid (Section 23-2). Riboflavin (vitamin B2) is a precursor of flavin adenine nucleotide FAD, a coenzyme in redox processes rather like NAD (Section 15-6C). Another example of a coenzyme is pyri-doxal (vitamin B6), mentioned in connection with the deamination and decarboxylation of amino acids (Section 25-5C). Yet another is coenzyme A (CoASH), which is essential for metabolism and biosynthesis (Sections 18-8F, 20-10B, and 30-5A). 

Moc-Thr(OTBDMS)p(OMe)2 Oxidative Decarboxylation of Amino Acids Derivatives and Synthesis of l-Aminoalkylphosphonic Acid Esters 28 Typical Procedure 148 ... 

Monig J, Chapman R, Asmus K-D (1985) Effect of the protonation state of the amino group on the OH radical induced decarboxylation of amino acids in aqueous solution. J Phys Chem 89 3139-3144... 

Poupko R, Rosenthal I, Elad D (1973) Photochemical decarboxylation of amino acids in the presence of metal ions. Photochem Photobiol 17 395-402... 

Biogenic amines in wine and fermented foods are formed primarily via the microbial decarboxylation of amino acids. Examples, such as histamine, tyramine, and phenylethylamine are toxic, especially in alcoholic beverages. Ethanol can inhibit the monoamino oxidase responsible for amine detoxification (Maynard and Schenker, 1996). Histamine can induce allergenic reactions in humans, such as rashes, edema, headaches, hypotension. Tyramine and phenylethylamine can cause hypertension and other symptoms related to the release of noradrenaline. 

As a biogenic amine, dopamine belongs to a group of substances produced in the organism by decarboxylation of amino acids. Besides dopamine and norepinephrine formed from it, this group includes many other messenger molecules such as histamine, serotonin, and y-aminobutyric acid. 

Finally, the decarboxylation of amino acids catalyzed by several pyridoxal phosphate-dependent enzymes has been shown to proceed by a retention of configuration at the Ca atom144. The stereochemical course of the decarboxylation of 5-hydroxy tryptophan to 5-hydroxytryptamine (serotonin) catalyzed by the pyridoxal phosphate-dependent aromatic L-amino acid decarboxylase (equation 15) exemplifies such studies145. 

Barton, D.H.R., Herve, Y, Potier, R, and Thiery, J. 1984. Reductive radical decarboxylation of amino-acids and peptides. J Chem Soc Chem Commun 1298-1299. 

The decarboxylation of amino acids is facilitated by copper Lewis acids. Treatment of tryptophan with copper(II) acetate in HMPA afforded tryptamine 117 in 45 % yield (Sch. 26) [58]. Chelation is thought to activate the carboxylate for elimination. The stable chelate can be isolated and undergoes decarboxylation when heated. An asymmetric version of a similar decarboxylation of malonate derivatives has been reported poor selectivity resulted from addition of chiral alkaloids [59]. 

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