Amino acid, oxidation

These include the mitochondrial respiratory chain, key enzymes in fatty acid and amino acid oxidation, and the citric acid cycle. Reoxidation of the reduced flavin in oxygenases and mixed-function oxidases proceeds by way of formation of the flavin radical and flavin hydroperoxide, with the intermediate generation of superoxide and perhydroxyl radicals and hydrogen peroxide. Because of this, flavin oxidases make a significant contribution to the total oxidant stress of the body. 

Most of the applications so far focus on the production of the chiral amino acid as the end product. Conversion of the chiral amino acid into the prochiral oxoacid as the end product is less common, although, for instance, Odman etal describe the use of GDH to convert L-glutamate into the higher-value 2-oxoglutarate. Similarly, Findrik et al describe in some detail the kinetics of quantitative conversion of L-methionine into 2-oxo-4-methylthiobutyric acid. In view of the relatively unfavorable equilibrium for amino acid oxidation, thermodynamic and kinetic considerations have to be carefully balanced. A high pH favors oxidative deamination, and fortunately also the PheDH has an unusually high pH optimum, above 10. However, this in itself will not secure... 

The situation is, however, different in starvation. In this condition, it is the degradation of muscle protein that provides the amino acids for gluconeo-genesis, so that all the oxo-acids generated (except those for lysine and lencine) are nsed to synthesise the glucose required for oxidation by the brain. Hence, a process other than amino acid oxidation mnst generate the ATP required by gluconeogenesis. This process is fatty acid oxidation. 

In lean subjects, amino acid oxidation, via glucose formation and glucose oxidation, provides almost four times more energy than in the obese snbjects (Table 16.4). That is, the obese lose protein mnch more slowly, which may be an important factor favouring survival of the obese in starvation. This is consistent with the fact that, from the data available, obese subjects have survived starvation approximately fonr times longer than the lean (abont 300 days versns 60-70 days Table 16.5). 

Tablel6.4 The contribution of amino acid oxidation to total energy reguirement during starvation in lean and obese subjects...

In normal young children, the contribution of amino acid oxidation to energy requirement in starvation is about 1%, similar to that in the obese. In malnourished children, who have a protein-energy deficiency, it is even lower (4%). This suggests that a mechanism exists to protect muscle protein from degradation in children. Such a mechanism may involve a faster and greater increase in ketone body formation in children compared with adults (Chapter 7). 

Chapter 18 Amino Acid Oxidation and the Production of Urea... 

Many of the biochemical processes that generate chemical energy for the cell take place in the mitochondria. These organelles contain the biochemical equipment necessary for fatty acid oxidation, di- and tricarboxylic acid oxidation, amino acid oxidation, electron transport, and ATP generation. In this experiment, a mitochondrial fraction will be isolated from beef heart muscle. The mitochondria will be analyzed for protein content and fractionated into submitochondrial particles. Each fraction will be analyzed for malate dehydrogenase and monoamine oxidase activities. 

Hawkins CL, Davies MJ (2005) The Role of Aromatic Amino Acid Oxidation, Protein Unfolding, and Aggregation in the Hypobromous Acid-Induced Inactivation of Trypsin Inhibitor and Lysozyme. Chem Res Toxicol 18 1669... 

Heterocyclic aroma compounds found in meat primarily arise from interactions between mono- and dicarbonyl compounds, H2S and ammonia. The carbonyl compounds are derived from the Maillard reaction, including Strecker degradation of amino acids, oxidation of lipids and aldolization reactions. H2S is produced by thermal degradation of sulfur amino acids and ammonia by amino acid pyrolysis. 

Mulholland, M.R., Glibert, P.M., Berg, GM., van Heukelem, L., Pantoja, S., and Lee, C. (1998) Extracellualar amino acid oxidation by microplankton A cross-ecosystem comparison. Aquat. Microb. Ecol. 15, 141-152. 

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