Metabolism of Ammonia and Nucleic Acids

Ammonia is generated mainly from the metabolism of amino acids and from the catabolism of purine and pyrimidine bases, which are produced from nucleic acids. Since it is toxic, it must be converted to a non-toxic compound for excretion from the body. This is achieved via the ornithine cycle, more usually known as the urea cycle. 

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CH 10 METABOLISM OF AMMONIA AND NUCLEIC ACIDS Table 10.5 Changes in the concentration of various intermediates of the urea cycle or their metabolites in plasma or urine in various enzyme deficiency diseases in humans ... 

Nitrogen (N) is a component of many biomolecules, especially of proteins and nucleic acids. Molecular N is reduced by certain free-living and symbiotic microorganisms (see Nitrogen fixation) to ammonia, which is the first and final product of nitrogen metabolism. 

The ratio of oxygen uptake to ammonia excretion in Black Sea mussels has been found to exhibit a distinct daily rhythm (Slatina, 1986). As a rule, the ammonia coefficient (O/N) tends to increase greatly at night. As this rise in energy metabolism does not result from an enhanced locomotor activity, it is difficult to explain or to find any analogue in fish. Farbridge and Leatherland (1987) demonstrated a strong effect of the lunar cycles on amino acid uptake by the scales, also on nucleic acids, metabolic reserves and plasma thyroid hormones in coho salmon. 

As reported in 1902, the substrate scope of the Dimroth triazole synthesis was limited to aromatic azides. An early extension of this methodology was reported in 1956 by Hoover and Day at the University of Pennsylvania. IH-1,2,3-Triazoles were of particular interest at the time as potential modifiers of nucleic acid metabolism. As part of a program directed at cancer chemotherapies, they replaced the azide aromatic moiety with a benzyl substituent. Sodium ethoxide-promoted reaction of benzyl azide (19) with active methylene compounds 25 provided 1-benzyl-1,2,3-triazoles 26 that could undergo reductive cleavage with sodium in liquid ammonia to afford the desired 4,5-disubstituted species. While various active methylene compounds were successfully used (ethyl cyanoacetate, cyanoacetamide, cyanoacetic acid, and malononitrile), the yields were low to modest when compared with aromatic substrates. ... 

The administration of N -2,6-diaminopurine resulted in the appearance of in RNA and DNA guanine, and in adenine to a lesser degree (203). Later studies with C -2,6-diaminopurine showed that only the guanine, and not the adenine was labeled (204). The incorporation of N into adenine in the first instance was probably due to purine synthesis from labeled ammonia, which would have been formed from catabolism of the administered labeled compound. Since 2,6-diaminopurine has not been found as a natural product, it is difficult to evaluate its metabolic importance in the conversion of dietary adenine to nucleic acid guanine. 

The synthesis of virus protein has not been worked out in any such detail as has that of nucleic acid. The only information comes from 3 sources (1) chemical balance studies already reviewed, (2) tracer studies of the origin of the N of T6 and T7 phages (160,163,262), and (3) a single investigation of the metabolism of lysine in cells infected with T6 (287). From the origin experiments it was found that a very small fraction of the protein N of T6 was derived from the host cell. This indicates that most of the virus protein is formed from extracellular ammonia by a... 

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