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High-Yield Terms
Aminotransferase: any of a family of enzymes that catalyze the transfer of an amino group between a α-amino acid and an α-keto acid
AST and ALT: aspartate aminotransferase (AST; also called serum glutamate-oxaloacetate aminotransferase, [SGOT]) and alanine transaminase (ALT; also called serum glutamate-pyruvate aminotransferase [SGPT]), the two prevalent liver enzymes whose elevations in the blood have been used as clinical markers of tissue damage
Glucose-alanine cycle: mechanism for skeletal muscle to eliminate nitrogen while replenishing its glucose supply. Glucose oxidation produces pyruvate which can undergo transamination to alanine; the alanine then enters the blood stream and is transported to the liver where it is converted back to pyruvate, which is then a source of carbon atoms for gluconeogenesis
Urea: nitrogen compound composed of 2 amino groups (−NH2) joined by a carbonyl (−C=O) functional group; is the main nitrogen-containing substance in human urine
Kwashiorkor: an acute form of childhood protein-energy malnutrition with adequate caloric intake; characterized by edema, irritability, anorexia, ulcerating dermatoses, and an enlarged liver with fatty infiltrates
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Nitrogen Distribution From Biosphere
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Humans are totally dependent on other organisms for converting atmospheric nitrogen into forms available to the body. Nitrogen fixation is carried out by bacterial nitrogenases forming reduced nitrogen, NH4+, which can then be used by all organisms to form amino acids (Figure 29-1).
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Reduced nitrogen enters the human body as dietary free amino acids, protein, and the ammonia produced by intestinal tract bacteria. A pair of principal enzymes, glutamate dehydrogenase and glutamine synthetase, incorporates this ammonia into carbon skeletons generating the amino acids glutamate and glutamine, respectively. Amino and amide groups from these 2 amino acids are then freely transferred to other carbon skeletons by transamination (Figure 29-2) and transamidation reactions.
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Aminotransferases exist for all amino acids except threonine and lysine. The most common compounds involved as a donor/acceptor pair in transamination reactions are glutamate and α-ketoglutarate (2-oxoglutarate), which participate in reactions with many different aminotransferases. Serum aminotransferases AST and ALT have been used ...