With amino acids, deamination

When oxides of nitrogen come in contact with water, both nitrous and nitric acids are formed (18) (Table IV). Toxic reactions may result from pH decrease. Other toxic reactions may be a consequence of deamination reactions with amino acids and nucleic acid bases. Another consideration is the reactions of oxides of nitrogen with double bonds (Table IV). The cis-trans isomerization of oleic acid exposed to nitrous acid has been reported (19). Furthermore, the reaction of nitrogen dioxide with unsaturated compounds has resulted in the formation of both transient and stable free radical products (20, 21) (Table V). A further possibility has been raised in that nitrite can react with secondary amines to form nitrosamines which have carcinogenic properties (22). Thus, the possible modes of toxicity for oxides of nitrogen are numerous and are not exhausted by this short list. 

Amino acids are quickly deaminated by L-ascorbic acid, leading to browning reactions (66). In the presence of oxygen, iron, and ascorbic acid or DHA, the amino acids gave ammonia, carbon dioxide, and an aldehyde with one carbon less than the original acid (67,68). The aldehydes are isolated as dimedone derivatives and are useful for identification of the amino acids. In the presence of copper and UV light, the deamination is increased. The red color 69-73) formed upon reaction of DHA with amino acids was used for their detection. Recent studies (74-78) of the reaction of DHA with amino acids led to the isolation of a product that changes readily to a novel, stable, free radical species... 

Contrary to the case of free a-amino acids, deamination-substitution of esters of a-amino acids generally proceeds with racemization with excess inversion about the a-carbon atom. However, reaction of the ethyl ester of phenylalanine and its derivatives with sodium nitrite in trifluoroacetic acid affords substitution products with retention of configuration and migration products with inversion of configuration. This result may be explained by assuming initial formation of the phenonium intermediate (2 Scheme 6). ... 

Attachment to Amino Group. The electron reacts with the protonated terminal amino group in aliphatic amino acids, leading to deamination (53,58). The rate constants in solution depend on pH, k decreasing as pH is increased. ESR studies on electron reaction with amino acids in neutral glasses at —196 °C indicate that dissociative attachment readily occurs producing a fatty acid radical ... 

Microorganisms and some plant tissues are capable of catalyzing a multiplicity of nonoxidative amino acid deamination reactions. It is beyond the scope of this chapter to review these systems, since for the most part they have not been studied with cell-free preparations. Two exceptions to the latter statement are the aspartase and tryptophanase systems. The latter is discussed in the chapter, Carbon Catabolism of Amino Acids. 

The amount of an enzyme present in a cell at any given time depends on the balance between the rate of its synthesis and breakdown. Different enzymes have very different half-lives ranging from a few minutes to several days (page 286). Those with short half-lives are inducible and repressible, i.e. their rates of synthesis and/or breakdown, and hence the level in the cell, are readily altered in response to environmental factors. Some enzymes are very sensitive to the nutritional state. Thus, many of those concerned with amino acid breakdown are afrected by the supply of amino acids as well as by hormonal factors. The changes are particularly large in the case of the aminotransferases that are responsible for the deamination of the essential amino acids. These enzymes virtually disappear when the protein intake is very low so that the essential amino acids are effectively conserved. The enzymes of the urea cycle are also significantly reduced. 

Deamination (Section 20.2) The removal of an amino group from a molecule, as occurs with amino acids during metabolic degradation. 

Early experiments by Borchers (1965) indicated that the supplementation with 1 g of thymol per 1 L of ruminal fluid in the presence of casein causes accumulation of amino acids and a decrease in the concentration of ammonia nitrogen, which snggests that amino acid deamination is hindered by ruminal bacteria. Broderick and Balthrop (1979) in their research conflrmed the inhibition of amino acid deamination resulting from the thymol supplementation. 

Reductive deamination of primary arylamines The amino substituent of an arylamine can be replaced by hydrogen by treatment of its derived diazonium salt with ethanol or with hypophosphorous acid. 

The NAD- and NADP-dependent dehydrogenases catalyze at least six different types of reactions simple hydride transfer, deamination of an amino acid to form an a-keto acid, oxidation of /3-hydroxy acids followed by decarboxylation of the /3-keto acid intermediate, oxidation of aldehydes, reduction of isolated double bonds, and the oxidation of carbon-nitrogen bonds (as with dihydrofolate reductase). 

When a cyclic /3-amino alcohol—e.g. 1—is treated with nitrous acid, a deamination reaction can take place, to give a carbenium ion species 2, which in turn can undergo a rearrangement and subsequent loss of a proton to yield a ring-enlarged cyclic ketone 3. This reaction is called the Tiffeneau-Demjanov reactionit is of wider scope than the original Demjanov reaction ... 

Protoadamantanone has been prepared by the nitrous acid deamination of 2-amino-l-adamantanol (77%), by aprotic diazo-tization of endo-7-aminomethylbicyclo[3.3.1]nonan-3-one in benzene with an equivalent amount of acetic acid (67%), and by thermolysis of 1-adamantyl hypohalites followed by base-promoted cyclization of the resulting halo ketones (32-37%)." In spite of low and erratic yields, the last reaction sequence has provided the most convenient route to the protoadamantanes, since the other two approaches require lengthy syntheses of the starting materials. 

Examples of flavoprotein enzymes include L-amino acid oxidase, an FMN-finked enzyme found in kidney with general specificity for the oxidadve deamination of... 

More-specific methods are available for identifying and quantitating the typical, amino sugar component of heparin (and some heparan sulfate species), namely, 2-deoxy-2-sulfoamino-D-glucose. Most of these methods are based on conversion of these residues into 2,5-anhydro-D-mannose by deamination with nitrous acid (see Section VIII,2). The 2,5-anhydro-D-mannose residues may be determined either colorimetrically,52-54 or fluorimetrically.55... 

Direct hydrogenation of amino acids to amino alcohols was first examined by Adkins et al. (3) via the esters, and recently studied by Antons and Beitzke in patents (4). Using Ru/C catalysts at high pressures (>14 MPa) and mild temperatures (70-150 °C), Antons demonstrated the conversion of carboxylic acids and amino acids with retention of optical activity in the product alcohols. High yields (>80%) and high enantiomeric purity (>97% in many cases) were achieved. Broadbent et al. had demonstrated earlier that under certain conditions hydrogenation of amino acids can be accompanied by deamination (8). 

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