Cycle, biochemical nitrogen

Our focus in this review is on the reactivity associated with the NOj reductases, which perform several steps in the biochemical cycling of nitrogen. Figure 4.1" " . These enzymes play key roles in the uptake and loss of agricultural fertilizers as well as the generation of atmospheric N2O, a potent greenhouse... 

Urea is a colorless, odorless crystalline substance discovered by Hilaire Marin Rouelle (1718—1779) in 1773, who obtained urea by boiling urine. Urea is an important biochemical compound and also has numerous industrial applications. It is the primary nitrogen product of protein (nitrogen) metabolism in humans and other mammals. The breakdown of amino acids results in ammonia, NH3, which is extremely toxic to mammals. To remove ammonia from the body, ammonia is converted to urea in the liver in a process called the urea cycle. The urea in the blood moves to the kidney where it is concentrated and excreted with urine. 

Biochemically, the pantothenate coenzymes are integral in the metabolism of carbohydrates, lipids, and nitrogen-containing compounds (185,186). They participate in the TCA or Krebs cycle, as well as fatty acid, phospholipid, sterol (cholesterol), and heme synthesis. The coenzymes mediate the exchange of 2-carbon (acetyl) and other acyl groups. They can serve as... 

Section M Smil, V. (1997) Global population and the nitrogen cycle. Sci. Amer. 277(7), 58-63. Warren, M.J., Cooper, J.B., Wood, S.P. and Shoolingan-Jordan, P.M. (1998) Lead poisoning, haem synthesis and 5-aminolaevulinic acid dehydratase. Trends Biochem. Sci. 23, 217-221. Warren, M.J. and Scott, A.I. (1990) Tetrapyrrole assembly and modification into the ligands of biologically functional cofactors. Trends Biochem. Sci. 15, 486-491. 

There are >40 distinct molybdenum enzymes that occur in all classes of living systems and are especially important in the biochemical cycles of carbon, nitrogen, and sulfur (24b). The majority of the molybdenum enzymes, with notable exceptions including the nitrogenases (25-28) and a 2-hydroxyglutaryl-CoA dehydratase (10), catalyze a conversion of the type [Eq. 1], that is, the net effect of the catalysis corresponds to the transfer of an oxygen atom to or from the substrate. 

W. G. Zumft, A. Viebrock, and H. Komer, Biochemical and Physiological Aspects of Denitrification, in The Nitrogen and Sulphur Cycles , eds. J. A. Cole and S. J. Ferguson, Cambridge University Press, Cambridge, 1988, p. 245. 

Mclnerney M. and Bolger T. (2000b) Temperature, wetting cycles and soil texture effects on carbon and nitrogen dynamics in stabilized earthworm casts. Soil Biol. Biochem. 32(3), 335-349. 

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