Urea and ammonia

The ammonia enters the portal vein and mixes with the metabolic nitrogen pool of the body. The fixation of this ammonia nitrogen into arginine, glutamic acid and utamine and aspartic acid represents a net contribution to nitrogen balance. The alternative fate of this ammonia is its conversion to urea prior to renal excretion. Thus the use of N-labelled ammonium salts or [ N]urea forms the basis of several common lines of clinical investigation. 

In another study this group of investigators have shown that urea nitrogen can be utilised for muscle protein synthesis in uraemic patients and that the administration of essential amino acids stimulated the utilization of nitrogen-containing metabolites for protein synthesis [330]. The N content of amino acids from hydrolysates of plasma and muscle protein following the intravenous administration of [ N]urea in ureamia, post-traumatic catabolism and in a normal subject were compared [331]. The distribution of label in amino acids supported the hypothesis that histidine is an amino acid which is essential in severe uraemia. 

Early studies showed that when rats were fed [ N]creatine it was deposited in the tissues and the extent of N-labelling of urinary creatinine indicated that it originated from creatine [338]. On feeding [ N]creatinine, rapid urinary excre- 

In a variety of clinical situations, it is important to have an estimate of muscle mass and to be able to monitor changes in this large protein pool. The most widely used method to obtain this estimate is based on a 24-h creatinine excretion [341]. The relationship found between daily creatinine output and muscle mass has been variously expressed by authors [342-344], though the validity of this procedure has been questioned [345]. 

The basis of this relationship is that urinary creatinine is the only degradation product of creatine phosphate [338] that cardiac and skeletal muscle contribute more than 90% of body creatine [346] and that creatine phosphate to creatinine degradation occurs at a fixed rate (non-enzymatically) [347]. Thus normally, the rates of formation and excretion of urinary creatinine would depend on the size and turnover rate of the creatine pool, and the relationship between muscle mass and creatine excretion would depend primarily on muscle creatine content. 

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A portion of the monophenylurea then reacts with the aniline (formed by the hydrolysis of the aniline hydrochloride or cyanate) to give diphenyl-urea and ammonia, a reaction which probably proceeds through the... 

ALkylenearnines, like AEP, react with urea [57-13-6] to form substituted ureas and ammonia (41). 

Urea Plants - In urea plants, wet scrubbers or fabrie filters are used to control fugitive emissions from prilling towers fabric filters are used to eontrol dust emissions from bagging operations. These equipment are an integral part of the operations, to retain product. New urea plants should achieve levels of particulate matter in air emissions of less than 0.5 kg/t of product for both urea and ammonia. 

Larrubia, M.A., Ramis, G. and Busca, G. (2000) An FT-IR study of the adsorption of urea and ammonia over V205-Mo03-Ti02 SCR catalysts, Appl. Catal. B, 27, L145. 

Figure A7A. Amino Group Removal for Elimination as Urea and Ammonia...

Calculated from the nitrogen in urea and ammonia which represents primarily protein metabolism (the nitrogen in nucleic acid is released as ammonia and converted to urea). 

At the proper temperature, the injected reagent reacts selectively in the presence of oxygen to reduce the oxides of nitrogen (NOJ primarily to molecular nitrogen (Nj) and water (FI2O). Figure 17.4 shows the results of pilot-scale tests of the use of urea and ammonia in the SNCR performance. 

Description Ammonia and carbon dioxide react at 150 bar to yield urea and ammonia carbamate. The conversion in the reactor is very high due to favorable NH3/CO2 ratio of 3.5 1 and operating temperature of 185°C to 190°C. These conditions prevent corrosion problems. Carbamate is decomposed in three stages at different pressures in the stripper at the same pressure as the reactor, in the medium-pressure decomposer at 18 bar and in the low-pressure decomposer at 4.5 bar. 

Guanidine is a soluble, crystalline compound and acts as a very strong base, as would be expected from the fact that it contains three ammonia residues, one of which, as an imino group, is in place of a carbonyl oxygen in urea or in carbonic acid. It readily absorbs carbon dioxide from the air. It is decomposed by barium hydroxide into urea and ammonia. 

FIGURE S.19 (A)Total urinary nitrogen and (B) urinary nitrogen as urea and ammonia. Totai urinary nitrogen decreases with transition from total fast to fructose-only fast. fRe-dravm with permission from Gelfand and Sherwin, 1 86 )... 

The protein requirement of the adult human was determined as follows. Ordinarily, the lequirement might be assumed to be equivalent to the amount of protein excreted in the form of urea and ammonia during the total fast. In the real world, however, humans consume carbohydrates. These carbohydrates arc usually present in abundance. Hence, calculation of the protein requirement uses, as a starting point, the value of the obligatory N losses with the carbohydrate-containing, protein-free diet. 

Catabolism of proteins and nucleic acids results in the formation of urea and ammonia—the so-called nonprotein nitrogenous compounds. 

Derivation (1) By heating urea and ammonia. The resulting mixture of isocyanic acid and ammonia reacts over a solid catalyst at approximately 400C to form melamine. (2) From cyanamide, dicyanamide, or cyanuric chloride. 

Nitrogen is eliminated from the body as urea and ammonia. Urea synthesized in the liver is excreted by the kidneys. Urinary ammonia is produced in the kidney. The nitrogen in other tissues is transported to the liver and kidney in... 

Uric acid, urea, and ammonia are among the most common nitrogenous waste molecules. 

Ough, C.S., Crowell, E.A., and Mooney, L.A. (1988). Formation of ethyl carbamate precursors during grape juice (Chardonnay) fermentation. I. Addition of amino acids, urea, and ammonia effects of fortification on intracellular and extracellular precursors, Am. J. Enol. Vitic., 39(3), 243-249. 

Metges CC, Petzke KH, El-Khoury AE, et al. 1999. Incorporation of urea and ammonia ntrogen into ileal and fecal microbial proteins and plasma free amino acids in normal men and ileostomates. Am J Clin Nutr 70(6) 1046-1058. 

The key role of insuhn in protein metabolism usually is evident only in diabetic patients with persistently poor glycemic control. Insulin stimulates amino acid uptake and protein synthesis and inhibits protein degradation in muscle and other tissues. The increased conversion of amino acids to glucose also results in increased production and excretion of urea and ammonia. In addition, there are increased circulating concentrations of branched-chain amino acids as a result of increased proteolysis, decreased protein synthesis, and increased release of branched-chain amino acids from the liver. 

The amounts are expressed in units generally reported by clinical laboratories. Note that the amounts for creatinine and uric acid are for the whole compound, whereas those for urea and ammonia are for the nitrogen content. 

Bradfield, P.M. Baggott, G.K. (1993). The effect of water loss upon the urate, urea and ammonia content of the egg of the Japanese quail Cotumix cotumix japonica. Comp. Bochem. Physiol, 106A, 187-93. 

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