Deamination, of amino acids

Strecker Degradation (Oxidative Deamination), Mild oxidizing agents such as aqueous sodium hypochlorite or aqueous A-bromosuccinimide, cause decarboxylation and concurrent deamination of amino acids to give aldehydes. 

Figure 11.3 is a flow model representing in extremely simple form the main relevant features of nitrogen metabolism. It is not difficult to propose a sufficient explanation why Bprot is isotopically heavier than the diet. We might expect that the net effect of transamination and deamination of amino acids is to remove isotopically lighter N (Macko et al. 1987). That is to say, we may expect that the equilibrium constant for the reaction ... 

The citric acid cycle is not only a pathway for oxidation of two-carbon units—it is also a major pathway for interconversion of metabolites arising from transamination and deamination of amino acids. It also provides the substtates for amino acid synthesis by transamination, as well as for gluconeogenesis and fatty acid synthesis. Because it fimctions in both oxidative and synthetic processes, it is amphibolic (Figure 16—4). 

Glycogenolysis and glycogen synthesis P-oxidation of fatty acids transamination and deamination of amino acids Cori cycle and glucose-alanine cycle, which recycles substrates between muscle and liver. 

B. Glutamate dehydrogenase the oxidative deamination of amino acids... 

Figure 24-10 Biosynthesis of citrulline, arginine, and urea. The green arrows indicate reactions directly involved in deamination of amino acids and the synthesis of urea. N from amino acids and C from C02 are traced in green.

Figure 24-11 Integration of the urea cycle with mitochondrial metabolism. Green lines trace the flow of nitrogen into urea upon deamination of amino acids or upon removal of nitrogen from the side chain of glutamine.

Thus far we have considered the deamination of amino acids and the fate of the resulting ammonium ion. The carbon skeleton remaining after deamination can be used in... 

Deamination of amino acids and nucleic acid bases. 

Amino acids are chemically reactive at their a-amino groups and their side chains. The carboxyl groups are relatively unreactive unless activated. A very useful reaction is the oxidative deamination of amino acids with ninhydrin. The reaction produces a blue pigment, which can be used for the detection of amino acids both qualitatively and quantitatively. The series of reactions producing the blue complex is given in Equation (4.2). 

The enzymes discussed in this paragraph are D- and L-amino acid oxidases, the presence of which has been detected in numerous organisms and tissues. They were only recently identified in bacteria and the corresponding enzymes were isolated (for a review see [54]). These enzymes are flavin adenine dinucleotide (FAD)-containing flavoproteins that catalyze the oxidative deamination of amino acids (Scheme 13.21). 

By (often photoinduced) oxidative deamination of amino acids (E (L) = -0.05 V) coordinated to Fe(III), these are converted to 2-oxocarboxylates or glyoxy-late and eventually oxalate (E (L) = -0.17 V)... 

The important reaction commonly employed in the breakdown of an amino acid is always the removal of its a-amino group. The product ammonia is excreted after conversion to urea or other products and the carbon skeleton is degraded to C02 releasing energy. The important reaction involved in the deamination of amino acids is... 

Precipitation of CaC03 is also promoted by ammonia which may be produced by organisms under both aerobic and anaerobic conditions. The most common reaction is oxidative deamination of amino acids which liberates ammonia according to eqn (10) ... 

Protein Metabolism The most important functions of the liver in protein metabolism are (1) deamination of amino acids for use as energy or conversion into fats and carbohydrates, (2) synthesis and interconversion of amino acids and other metabolically important compounds, (3) formation of urea for excretion of ammonia, and (4) formation of plasma proteins. 

Ammonia arises in the body principally from the oxidative deamination of amino acids. In addition to its uptake in the reactions mentioned above, ammonia is also excreted in the urine as ammonium salts. This is not derived directly from the blood ammonia but is formed by the kidney from glutamine by the action of glutaminase. In metabolic acidosis, ammonia production and excretion by the kidney is greatly increased, and conversely it is decreased in metabolic alkalosis. This may be an important means of excreting excess ammonia. It must be remembered that ammonia formed by the action of intestinal bacteria on the protein hydrolyzates in the intestine can be also absorbed. The contribution of the ammonia formed in this way to the total ammonia in the body is unknown. Since this ammonia drains into the portal circulation, it is promptly removed by the liver. 

It is difficult to estimate what the rate of the metal ion catalyzed oxidative deamination reaction of amino acids would be in natural waters. Hamilton and Revesz (30) found that the rate of oxidation of alanine in the presence of pyridoxal and manganese ions was inhibited by EDTA. Since metal ions in natural waters can be complexed by a variety of organic and inorganic compounds, their effectiveness in catalyzing the oxidative deamination of amino acids may be reduced. Also, the fraction of dissolved amino acids which would be complexed by metal ions at the pH and metal ion and amino acid concentrations found in natural waters must be considered. At neutral pH, where the amino group of the amino acid is protonated, the fraction of the amino acid that would be in the form of the metal ion complex depends upon the equilibrium constant for the formation of the complex and the pK of the amino proton of the amino acid. The reactions for the formation of the Cu2+-alanine complexes can be written as... 

In the urea cycle the toxic ammonium ions released by deamination of amino acids are incorporated in urea, which is excreted in the urine. 

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