Ammonia amino acid excretion

Photobiotechnology. Photosynthetic micro-organisms specifically designed for the production of compounds such as carotenoids, ammonia, amino-acids, H2 and possibly ethanol. Cyanobacteria, for example, are versatile micro-organisms whose growth and metabolism can be manipulated to preferentially excrete biochemicals. 

Excretion into urine of ammonia produced by renal mbu-lar cells facilitates cation conservation and regulation of acid-base balance. Ammonia production from intracellular renal amino acids, especially glutamine, increases in metabolic acidosis and decreases in metabolic alkalosis. 

The urea cycle is essential for the detoxification of ammonia 678 Urea cycle defects cause a variety of clinical syndromes, including a metabolic crisis in the newborn infant 679 Urea cycle defects sometimes result from the congenital absence of a transporter for an enzyme or amino acid involved in the urea cycle 680 Successful management of urea cycle defects involves a low-protein diet to minimize ammonia production as well as medications that enable the excretion of ammonia nitrogen in forms other than urea 680... 

This combination of reactions is known as transdeamination and is the mechanism for deamination of a number of amino acids (Table 8.9). The role of this process in catabolism is shown in Figure 8.10. The ammonia that is prodnced is converted, almost exclnsively, to urea for excretion. Becanse of the biochemical and clinical significance of ammonia, a whole chapter is devoted to it and to urea formation. 

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. 

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. 

Allantoin is the excretory product in most mammals other than primates. Most fish hydrolyze allantoin to allantoic acid, and some excrete that compound as an end product. However, most continue the hydrolysis to form urea and glyoxylate using peroxisomal enzymes.336 In some invertebrates the urea may be hydrolyzed further to ammonia. In organisms that hydrolyze uric acid to urea or ammonia, this pathway is used only for degradation of purines from nucleotides. Excess nitrogen from catabolism of amino acids either is excreted directly as ammonia or is converted to urea by the urea cycle (Fig. 24-10). 

Another form of detoxified ammonia that is used in nitrogen excretion is uric acid. Uric acid is the predominant nitrogen excretory product in birds and terrestrial reptiles (turtles excrete urea, whereas alligators excrete ammonia unless they are dehydrated, in which case they, too, excrete uric acid). Uric acid formed as a product of amino acid catabolism involves the de novo pathway of purine biosynthesis therefore, its formation from NH3 liberated in amino acid catabolism is described elsewhere (see chapter 23). In mammals, uric acid is exclusively an intermediate in purine... 

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. 

One of the pioneers of structured models in animal cell culture used a single-cell model (Batt and Kompala, 1989). Based on hybridoma metabolism (.Figure 8.6), the model was based on the formulation of four compartments amino acids (including the TCA precursors), the nucleotides (including DNA and RNA), the proteins, and lipids. The excreted byproducts (lactate and ammonia) and the excreted product (mAb) were also considered. However, although flexible for simulation of different... 

While the complete oxidations of fats and carbohydrates yield C02 + H20, the complete oxidation of amino acids yields C02 + H20 and as well as ammonia. Three fates of this so-called nitrogen waste product are common in animals it can be excreted into the outside medium (ammonotelism, which is common in many aquatic animals) it can be excreted as uric acid (uricotely, common in reptiles and birds) or, it can be excreted as urea (common... 

Proteins are likewise broken down by microorganisms, or eaten by mammals and hydrolyzed by enzymes to amino acids. These are further oxidized to NH3, H20, and C02, releasing energy. These inorganic compounds can be utilized by living organisms to synthesize proteins, or they can be excreted. Bacteria convert ammonia to nitrites and nitrates, which plants can convert to amino acids. 

Amino acids in excess of metabolic requirements are degraded to their carbon skeletons, which, as discussed in the preceding section, enter energy metabolism or are converted to other compounds and ammonia the ammonia is excreted as such or is converted to urea and then excreted. This is the situation with humans, but there are major species differences as to the means by which excess ammonia is removed. 

In aquatic animals, ammonia diffuses out of the body through the skin, but land animals excrete excess ammonia either as urea or uric acid. Ammonia is excreted by humans on high meat diets as a strategy to conserve Na+ and K +. Excess PO4- and SO4- produced from phosphoproteins and S-containing amino acids are excreted as ammonium salts Na+ and K+ are exchanged for NH in the kidney. The excretion of urea requires a plentiful supply of water, as it is normally excreted in solution, whereas uric acid is very insoluble and is excreted as a solid by birds and reptiles. Thus, in animals in which weight, or the conservation of water, is important (e.g., birds), excess ammonia is excreted as uric acid. 

In the fed state, when there is abundant protein and carbohydrate, dietary protein is hydrolyzed to amino acids. Those amino acids not required for protein synthesis are converted to 2-oxoacids by the aminotransferases. The 2-oxoacids are then converted into lipids and carbohydrate for storage. Glutamate dehydrogenase catalyzes the formation of ammonia from the excess amino groups derived from the amino acids this ammonia is excreted as urea. 

Most doctors use the plasma concentrations of creatinine, urea and electrolytes to determine renal function. These measures are adequate to determine whether a patient is suffering from kidney disease. Protein and amino acid catabolism results in the production of ammonia, which in turn is converted via the urea cycle into urea, which is then excreted via the kidneys. Creatinine is a breakdown product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body (depending on muscle mass). Creatinine is mainly filtered by the kidney, though a small amount is actively secreted. There is little to no tubular reabsorption of creatinine. If the filtering of the kidney is deficient, blood levels rise. 

One of the major products of amino acid metabolism is ammonia (NLI3), a molecule known to be highly toxic to higher organisms. In the liver, ammonia and carbon dioxide are used to produce a water-soluble form of nitrogen, urea, via the urea cycle. The liver passes this urea to the blood, which carries it to the kidneys to be filtered out and excreted in the urine. Since one function of the kidney is to collect and excrete urea, increases in the concentration of this compound in the blood are an indicator of poor kidney function. Since urea is formed in the liver, low blood urea nitrogen is often the consequence of impaired liver function due to disease or as the result of infection (hepatitis). 

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