Products of Amino Acid Degradation

Leu to acetoacetate and acetyl-CoA through transamination, decarboxylation, and a bunch of rearrangements lie to propionyl-CoA through transamination, decarboxylation, and a bunch of rearrangements Phe to Tyr, then to acetoacetate and fumarate Tyr to acetoacetate md fumarate 

Try to acetyl-CoA via ring oxidation and cleavage to ketoadipate Lys to acetyl-CoA via transamination and deamination to ketoadipate 

The nitrogen contained in the amino acids is usually disposed of through the urea cycle. One of the early, if not the first, steps in amino acid catabolism involves a transamination using oxaloacetate or a-ketoglutarate as the amino-group acceptor. This converts the amino acid into a 2-keto acid, which can then be metabolized further. 

These enzymes invariably involve a cofactor, pyridoxal phosphate (vitamin Bg). In addition, pyridoxal phosphate is also required for most decarboxylations, racemizations, or elimination reactions in which an amino acid is a substrate. Pyridoxal phosphate is not involved in decarboxylations in which the substrate is not an amino acid. So if a question 

Phosphorylation Glycogen Metabolic Movements of Glycogen Fat Metabolic Movements of Fat Protein Metabolic Movements of Protein Tissue Cooperation Liver Muscle Ketone Bodies 

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Nonessential Amino Acid Synthesis Essential Amino Acids Amino Acid Degradation Generalities of Amino Acid Catabolism Products of Amino Acid Degradation... 

The metabolic products of amino acid degradation are acetyl-CoA, acetoacetyl-CoA, pyruvate, a-ketoglutarate, succinyl-CoA, fumarate, and oxaloacetate. 

Within the moderately polar substances of the second extracts phenolic compounds were most abundant (see Fig. 2B). Next to p-cresol (260-12000 pg/L), a further product of amino acid degradation and putrefaction processes, the xenobiotic compound 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) was detected with concentrations up to 25000 pg/L in seepage water samples. The amount in the sample LW was significantly lower (4200 pg/L) indicating a rapid degradation of these phenols during... 

The ammonium ion, which is the end product of amino acid degradation, is toxic if it is allowed to accumulate. Therefore, a series of reactions, called the urea cycle, detoxifies ammonium ion (NH/) by forming urea, which is excreted in the urine. 

Alcohol is distilled up to a content of 96% in one or more stages. About 1 % of ethanol consists of fusel oils (degradation products of amino acids) which can be used as solvents for lacquers and resins. Solids from the processed liquor containing proteins, carbohydrates, mineral salts, riboflavin and other vitamins are used in poultry, swine and cattle feeds. C02 and H2 produced in butanol-acetone-butyric acid production can be used for the chemical synthesis of methanol and ammonia, or are burned. 

Aldehydes related to common amino acids (3-methylbutanal from leucine, 2-methylpropanal from valine, phenylacetaldehyde from phenylalanine) are formed by enzymatic decarboxylation of the corresponding keto acids, which in turn are reversibly related to the amino acids by transamination [i.e., the keto acids are both degradation products of amino acids 147, 148) and intermediates in their synthesis 149). A third possibility—non-enzymatic oxidation of amino acids to aldehydes by enzymatically produced o-quinones—is established 150, 151) but is not discussed here. 

PPi is made in three ways (1) in the nucleus as a by-product of RNA synthesis (nNTP —> NMPn + nPPi) (2) in the cytosol as a by-product of amino acid activation for protein synthesis (aa + ATP —> aaAMP + PPi) and (3) by acetyl CoA synthetase on the outer mitochondrial membrane prior to its degradation for ATP production (R-COOH + ATP + HS-CoA —> R-Co-SCoA + AMP + PPi). Amino acid activation is the major source of cytosolic PPi, which is transported by the ANK protein to the osteoid matrix to inhibit premature mineralization (see Sect. 9.3.5). 

Table 2-2. Structure of amino acid degradation/derivative products found in human hair. ...

The thermal generation of flavor is a very essential process for the "taste" of many different foodstuffs, e.g. cocoa, coffee, bread, meat. The resulting aromas are formed through non-enzymatic reactions mainly with carbohydrates, lipids, amino acids (proteins), and vitamins under the influence of heat. Thiamin (vitamin B ) and the amino acids, cysteine and methionine, belong to those food constituents which act as flavor precursors in thermal reactions. The role of thiamin as a potent flavor precursor is related to its chemical structure which consists of a thiazole as well as a pyrimidine moiety. The thermal degradation of this heterocyclic constituent leads to very reactive intermediates which are able to react directly to highly odoriferous flavor compounds or with degradation products of amino acids or carbohydrates. 

Extracellular free amino acids are usually those commonly found in protein. Some non-protein amino acids, such as y-aminobutyric acid and )8-amino acids, also occur. Low levels of )8-amino acids are usually products of nucleic acid degradation. 

In addition to sugars and their degradation products and the degradation products of amino acids (amines, ammonia and aldehydes), these reactions also include carbonyl compounds already present in foods as primary substances (e.g. aldehydes and ketones occurring in essential oils), ascorbic acid and carbonyl compounds formed in foods from precursors other than carbohydrates (aldehydes resulting from fat oxidation), thereby the reactions become even more complex. 

Significant aliphatic sulfur compounds are methional, 3-methyl-but-2-ene-1-thiol, 3-mercapto-3-methylbutan-l-ol (8-124), its ester 3-mercapto-3-methylbutyl formate, methanethiol and dimethyltrisulfide. 3-Mercapto-3-methyl-l-ol also occurs in passion fruit and blackcurrant, and as a putative cat pheromone in cat urine, where it is formed as a degradation product of amino acid L-felinine (see Section 2.2.1.2.2). Of more than 70 known pyrazines, the most important compounds in roasted coffee are isopropylpyrazine, 2-isobutyl-3-methoxypyrazine, 2-ethyl-3,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, 2,6-dimethyl-3-vinylpyrazine and 2-ethyl-6-methyl-3-vinylpyrazine. Pyridine and its alkyl derivatives and bicyclic pyridines have a negative impact on the quality of coffee aroma. Important aromatic... 

Protein content of lichens varies between 1.6 and 11.4% of the dry weight but can go as high as 20%. Methyl- and trimethylamine, amines that have been detected in various species of the Stictaceae, are apparently degradation products of amino acids. 

These proposed scenarios are consistent with conclusions from the literature on studies aimed at identifying conditions under which bacterial degradation is a sink or source for amino acid-like FDOM (Cammack et al., 2004 Stedmon and Markager, 2005b, Nieto-Cid et al., 2006 Biers et al., 2007). Both Cammack et al. (2004) and Nieto-Cid et al. (2006) proposed scenarios under which amino acid-like FDOM may accumulate and be subsequently consumed, as a function of nutrient availability. Consistently, Biers et al. (2007) showed production of amino acid-like FDOM during bacterial incubation in seawater when labile sources of nitrogen were added. The results from these studies can explain some of the conflicting trends that have been reported. 

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