Amino acid metabolism model

Pyridoxal phosphate is the coenzyme for the enzymic processes of transamination, racemization and decarboxylation of amino-acids, and for several other processes, such as the dehydration of serine and the synthesis of tryptophan that involve amino-acids (Braunstein, 1960). Pyridoxal itself is one of the three active forms of vitamin B6 (Rosenberg, 1945), and its biochemistry was established by 1939, in considerable part by the work of A. E. Braunstein and coworkers in Moscow (Braunstein and Kritzmann, 1947a,b,c Konikova et al 1947). Further, the requirement for the coenzyme by many of the enzymes of amino-acid metabolism had been confirmed by 1945. In addition, at that time, E. E. Snell demonstrated a model reaction (1) for transamination between pyridoxal [1] and glutamic acid, work which certainly carried with it the implication of mechanism (Snell, 1945). 

To conceptualize amino acid metabolism, it is useful to consider a model which describes the flux of amino acids through... 

Specific exercise such as weightlifting can increase muscle mass (9,10). While the potential to develop muscle mass is established, the metabolic changes that lead to these changes remain unclear. Relatively few studies have examined amino acid metabolism during exercise-induced hypertrophy. The primary reason for the lack of information is the absence of a convenient animal model for weightlifting studies. Human studies utilizing nonradioactive, stable isotopes have not yet been done. 

Matsuoka, C., Tanaka, N., Arakawa, Y. Beneficial effects of branched-chain amino acids on altered protein and amino acid metabolism in liver cirrhosis Evaluation in a model of liver cirrhosis induced in rats with carbon tetrachloride. Hepatol. Res. 2003 27 117-123... 

Abstract The diet of industrialised countries is usually rich in amino acids, which are partly used as a source of calories. However, metabolic alterations are observed in diseased patients and a preferential retention of Sulphurated Amino Acids (SAA) occurs during the inflammatory response. It has been demonstrated in an acute sepsis phase model in rats that the metabolism of L-Cysteine (Cys) is modified. Glutathione (GSH) concentration is greater in the liver, kidneys and other organs and Cys incorporation into proteins is higher in the spleen and lungs. In the plasma Acute Phase Proteins are released while Albumin is decreased. The pro-inflammatory cytokines such as Interleukin-1, lnterleukin-6 and TNF-a are the main initiators altering protein and amino acid metabolism. 

Haussinger D (1987) Isolated perfused rat liver an experimental model for studies on ammonium and amino acid metabolism. Infusionsther Klin Ernahr 14(4) 174-178... 

However, almost none of appropriate enzyme models have ever been reported for the reaction path control or the allosteric control in homogeneous aqueous solution(2). In biological systems, both control mechanisms are very frequently and significantly operating as in the case of the reaction path control of the amino acid metabolism by individual enzyme(3) or the allosteric control of levels of many important compounds by glutamine synthetase. 

Bier, D., Stable isotopes in biosciences, their measurement and models for amino acid metabolism. Eur. J. Pediatr, 156(Suppl. 1), S2-S8 (1997). 

Freiding, S., Gutsche, K.A., Ehrmann, M.A., and Vogel, R.F. (2011) Genetic screening of Lactobacillus sakei and Lactobacillus curvatus strains for their peptidolytic system and amino acid metabolism, and comparison of their volatilomes in a model system. SystAppl Microbiol 34, 311-320. 

This paper explores how models may be developed to account for the relationship between the stable isotope composition of a body tissue of an organism and its diet. The main approach taken is to express this relationship as an explicit equation, or a DIFF , and then to show how the values of such a DIFF can be evaluated from published experimental data. These values can be expected to have a much wider meaning than a simple encapsulation of a particular experimental design. As a main example, we show how the values may be used to constract a metabolic model in which the synthesis of non-essential amino acid for collagen construction can be treated. A second example is to show how the evaluation, in terms of diet, of the spacing between collagen and carbonate 6 C may be put on a rigorous basis. 

Figure 11.1. A flow-model scheme for treating the protein routing question. Labels refer to flow rates of carbon. The total carbon flux, into and out of the body, is 1, divided into F (for protein) and 1 - F for the remainder. The significant relevant internal fluxes are between the amino acid pool (coupled to the body protein pool), and the energy metabolism pool . The extent to which protein routing is observable in the body protein composition depends on the value ofX (See Fig. 11.2). Numbers in refer to suggested isotopic fractionations associated with a metabolic path, which are consistent with the data of the Ambrose and Norr (1993) and Tieszen and Fagre (1993) data set (see Section 4.1).

Figure 11.3 is a flow model representing in extremely simple form the main relevant features of nitrogen metabolism. It is not difficult to propose a sufficient explanation why Bprot is isotopically heavier than the diet. We might expect that the net effect of transamination and deamination of amino acids is to remove isotopically lighter N (Macko et al. 1987). That is to say, we may expect that the equilibrium constant for the reaction ... 

The synthesis in many extant organisms of these two amide residues from their respective precursors glutamate and aspartate esterified to tRNA (the indirect aminoacylation pathways described in Sections 5.14.3 and 5.14.4) and that of other amino acid residues, such as selenocysteine (which is also synthesized from a precursor esterified on a tRNA °) support the model of prebiotic metabolism taking place at the surface of solid particles, " analogous to ancestral RNAs. 

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