Nitrogen in amino acids

Figure 29-2. Overall flow of nitrogen in amino acid catabolism.

CD indicated. NH4 utilization was determined as indicated in Figure 2. The Casitone added to the medium represented about 30 mM nitrogen in amino acids plus peptides. ... 

A. The nitrogen in amino acids derived from protein is converted to urea and excreted in A the urine. 

The nitrogen in amino acids, purines, pyrimidines, and other biomolecules ultimately comes from atmospheric nitrogen, Nj. The biosynthetic process starts with the reduction of N2 to NH (ammonia), a process called fixation. The extremely strong N —N bond, which has a bond energy of 940 kjmol (225 kcal moP ), is highly resistant to chemical attack... 

While ammonia, derived mainly from the a-amino nitrogen of amino acids, is highly toxic, tissues convert ammonia to the amide nitrogen of nontoxic glutamine. Subsequent deamination of glutamine in the liver releases ammonia, which is then converted to nontoxic urea. If liver function is compromised, as in cirrhosis or hepatitis, elevated blood ammonia levels generate clinical signs and symptoms. Rare metabolic disorders involve each of the five urea cycle enzymes. 

Nitrogen-containing side chains in amino acids can be altered by oxidation forming chloramines or even become deaminated. The result is often the formation of carbonyls (e.g., aldehydes) and hydroxyls. Lee, S et al. (2006) found that Fe-EDTA-mediated oxidation of human... 

The nitrogen contained in the amino acids is usually disposed of through the urea cycle. One of the early, if not the first, steps in amino acid catabolism involves a transamination using oxaloacetate or a-ketoglutarate as the amino-group acceptor. This converts the amino acid into a 2-keto acid, which can then be metabolized further. 

Cu(II) impurity complexes in amino acid single crystals have been the subject of several EPR studies181-183. Since nitrogen and proton hf structures are only partially resolved in the EPR spectra, no detailed information about the electronic properties of the complex in the neighborhood of the metal ion can be evaluated. ENDOR spectroscopy has therefore been applied58,63 to draw detailed pictures of the positions and the molecular environment of Cu(II) impurities in amino acid crystals. 

Little attention has been paid to the question of inter-individual differences in amino acid requirements. In the attempts to determine what the human adult requirements for individual essential amino acids are (for maintaining nitrogen equilibrium), studies have been made on individual young men. The following inter-individual ranges... 

Glutamate can then participate in the formation of other amino acids via the process called transamination. Transamination is the exchange of the amino group from an amino acid to a keto acid, and provides the most common process for the introduction of nitrogen into amino acids, and for the removal of nitrogen from them. The reaction is catalysed by a transaminase enzyme, and the coenzyme pyridoxal phosphate (PLP) is required. 

Schoenberg R, Zink S, Staubwasser M, von Blanckenburg F (2008) The stable Crisotope inventory of solid Earth reservoirs determined by double-spike MC-ICP-MS. Chem Geol 249 294-306 Schoenheimer R, Rittenberg D (1939) Studies in protein metabolism I, General considerations in the application of isotopes to the study of protein metabolism. The normal abundance of nitrogen isotopes in amino acids, J Biol Chem 127 285-290... 

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