Nitrogen metabolism overview

Blevins, D.G. (1989). An overview of nitrogen metabolism in higher plants. Recent Advances in Phytochemistry 23, 1-41. 

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.

NITROGEN FIXATION AND AGRICULTURE Amino Acid Metabolism Overview Reactions of Amino Groups Synthesis of the Amino Acids... 

For the quantitative description of the metabolic state of a cell, and likewise which is of particular interest within this review as input for metabolic models, experimental information about the level of metabolites is pivotal. Over the last decades, a variety of experimental methods for metabolite quantification have been developed, each with specific scopes and limits. While some methods aim at an exact quantification of single metabolites, other methods aim to capture relative levels of as many metabolites as possible. However, before providing an overview about the different methods for metabolite measurements, it is essential to recall that the time scales of metabolism are very fast Accordingly, for invasive methods samples have to be taken quickly and metabolism has to be stopped, usually by quick-freezing, for example, in liquid nitrogen. Subsequently, all further processing has to be performed in a way that prevents enzymatic reactions to proceed, either by separating enzymes and metabolites or by suspension in a nonpolar solvent. 

This text is divided into seven parts part l, An Overview of Biochemical Structures and Reactions That Occur in Living Systems part 2, Protein Structure and Function part 3, Catalysis part 4, Metabolism of Carbohydrates part 5, Metabolism of Lipids part 6, Metabolism of Nitrogen-Containing Compounds and part 7, Storage and Utilization of Genetic Information. 

An Overview of Nitrogen and Carbon Assimilation and Metabolism in Roots and Nodules of N2 Fixing Plants... 

Figure 9.1 shows an overview of protein metabolism in addition to the dietary intake of about 80 g of protein, almost the same amount of endogenous protein is secreted into the intestinal lumen. There is a small faecal loss equivalent to about 10 g of protein per day the remainder is hydrolysed to free amino acids and small peptides, and absorbed (section 4.4.3). The faecal loss of nitrogen is partly composed of undigested dietary protein, but the main contributors are intestinal bacteria and shed mucosal cells, which are only partially broken down, and the protective mucus secreted by intestinal mucosal goblet cells (see Figure 4.2). Mucus is especially resistant to enzymic hydrolysis, and contributes a considerable proportion of inevitable losses of nitrogen, even on a protein-free diet.

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