The Metabolism of Nitrogen

Atmospheric nitrogen (Ng) is not highly reactive, but it must be converted to ammonia or to nitrates to be biologically useful, first to plants, then to animals. 

Nitrogen compounds in the biosphere include amino acids, purines, and pyrimidines. Their pathways for biosynthesis and breakdown tend to be long and complex. 

Sign in at www.thomsonedu.com/login to test yourself on these concepts. 

The topic of nitrogen metabolism includes the biosynthesis and breakdown of amino acids, purines, and pyrimidines also, the metabolism of porphyrins is related to that of amino acids. Many of these pathways, particularly the anabolic ones, are long and complex. In discussing pathways in which the amount of material is large and highly detailed, we shall concentrate on the most important points. Specifically, we shall concentrate on overall patterns and on interesting reactions of wide applicability. We shall also be interested in health-related aspects of this material. Other reactions will be found at the BiochemistryNow Interactive website for this text. It can be considered a repository of supplementary material for this chapter, and we shall refer to it a number of times. 

Root nodules of leguminous plants play a pivotal role in nitrogen fixation. 

---

Chapters 12-16, 17-23 Organization of carbohydrate metabolism, lipid metabolism, and the metabolism of nitrogen-containing compounds, respectively, into self-contained units. 

Several other proteins show a low, but significant amino acid identity with atzA (Table 22.4). All of these, urease-alpha subunit (urea amidohydrolase), cytosine deaminase, and imidazolone-5-propionate hydrolase, catalyze hydrolytic reactions with substrates involved in the metabolism of nitrogenous compounds (Sadowsky et al 1998). A Rhizobium strain capable of atrazine dechlorination has been isolated from a soil that was previously treated with atrazine (Bouqard et al., 1997). This bacterium could not mineralize atrazine, and it accumulated hydroxyatrazine as the sole metabolite after long-term incubations. Interestingly, 22 of the 24 identified amino acids at the N-terminus of the atrazine halidohydrolase from Rhizobium were identical with atzA from Pseudomonas strain ADP. 

Figure 7-1. Overview of nitrogen metabolism. The metabolism of nitrogen-containing compounds is shown in bold face type on the right, and that of glucose and fatty acids is shown in light face on the left. aKG = a-keto-glutarate ETC = electron transport chain OAA = oxaloacetate G-6-P = glucose 6-phosphate G-1-P= glucose 1-phosphate.

Kurien, P. P., Narayanarao, M., Swaminathan, M., and Subrahmanan, V. (1960). The metabolism of nitrogen, calcium and phosphorus in undernourished children. 6. The effect of complete replacement of rice in poor vegetarian diets by kaffir com (Sorghum vulgare). Br.. Nutr. 14, 339-345. 

---