A-Amino nitrogen

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. 

ANIMALS CONVERT a-AMINO NITROGEN TO VARIED END PRODUCTS... 

Synthesis of 1 mol of urea requires 3 mol of ATP plus 1 mol each of ammonium ion and of the a-amino nitrogen of aspartate. Five enzymes catalyze the numbered... 

Figure 29-8. The glutaminase reaction proceeds essentially irreversibly in the direction of glutamate and NH/ formation. Note that the amide nitrogen, not the a-amino nitrogen, is removed.

Removal of a-amino nitrogen by transamination (see Figure 28-3) is the first catabolic reaction of amino acids except in the case of proline, hydroxyproline, threonine, and lysine. The residual hydrocarbon skeleton is then degraded to amphibolic intermediates as outhned in Figure 30-1. 

Hall et at. 300) described an indirect method for the determination of urinary a-amino nitrogen. Copper is solubilized from insoluble copper phosphate by complexing with a-amino groups at slightly alkaline pH. The remaining copper phosphate is removed by filtration and the filtrate is diluted 1 10 or 1 20 with 0. IN hydrochloric acid to measure the dissolved copper by atomic absorption. Standards are prepared using alanine. 

Hofsten and Lalasidis (15), however, reported that plasteins subjected to gel exclusion chromatography in 50X acetic acid showed no increase in molecular size over that of the reactants. Monti and dost (29) reached the same conclusion based on gel chromatography in DMSO and on analysis of a-amino nitrogen in plasteins. Hofsten and Lalasidis (15) noted that hydrophobic peptides showed unusual elution behavior on sephadex gels in water or dilute buffers, providing a possible explanation for differences in their results compared to those of Arai et al. 

Nitrogen values more than triple on adding ammonium nitrate. The mor the straw is rotted, the less nitrogen can be hydrolyzed with hydrochloric acid. A part of the nitrogen in the lignin fractions is fixed as a-amino nitrogen. The quantity decreases from 60% of total nitrogen content in fresh straw to about 20% in rotted straw. A remarkable decrease could be observed for the methoxyl content. This fact can be explained by an enzymatic demethylation process. 

Vertebrates obtain most of their amino acids by nutrition. Amino acid degradation in vertebrates usually starts with the loss of the a amino nitrogen and finishes with the return of the carbon skeletons to the central metabolic pathways. 

Degradative pathways for most amino acids begin by removal of the a-amino nitrogen. There are two major routes of deamination Transamination and oxidative deamination. 

C4N The C4N unit is usually found as a heterocyclic pyrrolidine system and is produced from the non-protein amino acid L-ornithine. In marked contrast to the Q-,C2N and indole.C2N units described above, ornithine supplies not its a-amino nitrogen, but the 8-amino nitrogen. The carboxylic acid function and the a-amino nitrogen are both lost. 

If A-amino nitrogen heterocycles are used as the hydrazine component, cyclic hydrazone dyes are obtained whose absorption maximum is shifted bathochromi-cally with respect to the open-chain hydrazone dyes [38], The dye 15 dyes polyacrylonitrile fibers a clear bluish red shade ... 

According to data obtained in our laboratory by Soupart (S24) (see Section 3.1), the results are lower still among 15 normal adults of both sexes they vary between 0.35 and 1.18g/24hr, with an average level of the order of 0.8 g in terms of a-amino nitrogen, the corresponding excretion levels are 41-133 mg/24 hr, with an average of the order of 90 mg. 

According to H. Loeb, when the size of the sample is based on its a-amino nitrogen content rather than on its total nitrogen content, the chromatograms look very different (unpublished observations). 

Assay (Total Nitrogen TN) Not less than 4.0%. a-Amino Nitrogen (AN) Not less than 3.0%. a-Amino Nitrogen/Total Nitrogen (AN/TN) Percent Ratio Not less than 62.0% and not more than 85.0% when calculated on an ammonia nitrogen-free basis. 

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