Decarboxylation reactions amino acids

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... 

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... 

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-... 

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. 

The carbonyl-assisted decarboxylation ofa-amino acids is closely related to an important reaction a decarboxylative transamination of N-unsubstituted o(-amino acids. It has been widely accepted that this decarboxylative transamination proceeds through the initial formation of imine carboxylic... 

Reaction with ninhydrin Ninhydrin is a strong oxidizing agent. When a solution of amino acid is boiled with ninhydrin, the amino acid is oxidatively deaminated to produce ammonia and a ketoacid. The keto acid is decarboxylated to produce an aldehyde with one carbon atom less than the parent amino acid. The net reaction is that ninhydrin oxidatively deaminates and decarboxylates a-amino acids to C02, NH3 and an aldehyde. The reduced ninhydrin then reacts with the liberated ammonia and another molecule of intact ninhydrin to produce a purple coloured compound known as Ruhemann s purple. 

Amines are produced by decarboxylation of amino acids in reactions that utilize pyridoxal phosphate as a cofactor. 

Another PLP-catalyzed reaction is decarboxylation of amino acids (Fig. 8.35). These are part of the biosynthesisof neurotransmitters, includ-... 

Degradation Reactions. Oxidative decarboxylations of amino acids serve as a good example. Schizophyllum commune is capable of degrading phenylalanine to phenylacetic acid as well as other acids. 

The decarboxylation of amino acids generally involves pyridoxal 5 -phosphate (PLP) as a cofactor (101-104) (Editor s note For additional features of PLP-dependent decarboxylation, see Chapter 7 by Kluger.). The general reaction is shown in Eq. (17),... 

Bi, thiamin oxidation-reduction potentials, hydroxylation reactions that require copper or iron Oxidative decarboxylation of amino acids,... 

The decomposition of these intermediates leads to the formation of ene-diols, also known as reduc-tones, in redox equilibrium with a-dicarbonylated compounds. These are responsible for the oxidation of plant tissues. The a-dicarbonylated compounds resulting from the rearrangement of the Amadori and Heyns intermediates may in turn add amino acids from must and wine (Figure 8.28). The corresponding addition products develop by intramolecular decarboxylation, according to the well-known Strecker breakdown reaction. Amino acids that become involved in this reaction ultimately become aldehydes. 

Figure 11.13 Reactions at a-carbon of a-amino acids catalyzed by pyridoxal enzymes All three substituents at C are subject to labilization in the three types of a-carbon reactions. The hydrogen is labilized in recemization reactions, the amino group is labUized in the transamination and the carboxyl group is labilized in decarboxylation. a-Amino acid condenses with pyridoxal phosphate to yield pyridoxylidene imino acid (an aldimine). The common intermediate, aldimine and distinct ketimines leading to the production of oxo-acid (in transamination), amino acid (in racemization) and amine (in decarboxylation) are shown. The catalytic acid (H-A-) and base (-B ) are symbolic both can be from the same residue such as Lys258 in aspartate aminotransferase.

This reaction is useful for the conversion of carboxylic acids into alcohols with one less carbon, and the decarboxylation of amino acids and polypeptides. 

The decarboxylation of amino acids is a key step in the synthesis of neurotransmitter amino compounds and other physiologically important compounds. The enzyme PLP forms an internal aldimine with the a-amino group of a specific Lys residue. The obligatory first chemical step in all PLP-dependent enzymatic reactions is the formation of an SB intermediate (aldimine) between the coenzyme aldehyde and the substrate amino group. The general utility of PLP is derived from its ability to stabilize the carbanions generated adjacent to the SB in the external aldimine intermediate... 

Belleau and Burba (1960) have used Streitwieser s asymmetric reduction method to establish the stereochemistry of the en-Z3rmatic decarboxylation of amino acids. Reduction of p-methoxy-phenylacetaldehyde with 1-deuteroisobornyloxy magnesium bromide yielded p-methoxyphenethyl-l-d alcohol. The alcohol was converted to i -l-ci-tyramine via the tosylate and azide. The fact that enzymatic decarboxylation of S-tyrosine in D2O also yields 12-l-(i-tyramine shows that this reaction proceeds with retention of configuration (Fig. 10). 

The formation of amines corresponding to certain amino acids has been known for a century, and for over 50 years it has been known that certain amino acids can be decarboxylated by animal and microbial preparations. Hanke and Koessler found that various strains of E. colt contained decarboxylases for different amino acids, and that the ability to decarboxylate individual amino acids was so distributed among strains as to indicate that specific enzymes existed for the decarboxylation of each of the susceptible amino acids. The reactions of amino acid decarboxylases are illustrated in Fig. 31. 

V. MECHANISMS FOR THE BREAKDOWN OF AMINO ACIDS A. General Mechanisms (a) Decarboxylation of Amino Acids In the presence of decarboxylases amino adds give CO, and an amine according to the general reaction ... 

This coenzyme occupies a unique position, in that it is involved in at least four types of reactions which all appear to be quite different. These are the decarboxylation of amino acids, transamination, and the synthesis and cleavage of tryptophan. However, all these reactions, as we shall see, have one thing in common they involve an a-amino acid and are concerned with either the amino group or the carbon atom adjacent to the amino group. 

In the tissues, vitamin Be occurs predominantly as the phosphate of pyridoxal or pyridoxamine, especially the former, except in the liver. Pyri-doxal phosphate functions as a coenzyme in four types of reactions decarboxylation of amino acids, transamination, and the synthesis and cleavage of tryptophan (Chapter 19). This coenzyme is necessary for the deamination of amino acids and for the formation of urea nitrogen. It appears to be essential for the conversion of tryptophan to the pyridine coenzymes. Pyridoxine may be related to fatty acid metabolism and seems to be necessary for normal adrenal cortical function. ... 

Some enzymatic reactions that involve PLP include transaminations, which convert amino acids to ketones for use in the citric acid cycle and other pathways decarboxylation of amino acids for biosynthesis of neurotransmitters such as histamine, dopamine, and serotonin and inversion of amino acid chirality centers, such as required for the biosynthesis of cell walls in bacteria. 

Not only aldehydes (cf. 5.3.1.1), but also amines are formed in the Strecker reaction (cf. 4.2.4.4.T). The odor thresholds of these amines (examples in Table 5.26) are pH dependent. The enzymatic decarboxylation of amino acids produces the same amines as the Strecker reaction the precursors are shown in Table 5.26. Both reactions take place e. g. in the production of cocoa, but the Strecker... 

Primary amines in foods most often arise as products of enzymatic reactions that include decarboxylation of amino acids catalysed by non-specific decarboxylases or enzymatically catalysed amination or transamination of aldehydes (Figure 8.69). 

Decarboxylation of amino acids can also proceed as a non-enzymatic reaction. Analogously to the enzyme catalysed decarboxylations, amines are formed as byproducts of the Strecker degradation of amino acids and by thermal decarboxylation of amino acids, especially of sulfur amino acids, hydroxyamino acids and aromatic amino acids. For example, thermal decarboxylation and subsequent reactions of cysteine and cystine produce ammonia... 

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