Amino acid pools

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).

We know, as the measured values of dp and dN (from the DIFF in Section 2.4) imply, that isofractionation takes place within the organism. To include fractionation in the model, the fractionating steps must be made explicit. The simplest arrangement, consistent with observation, is as labeled in Fig. 11.2. That is, a fractionation of +2.5%o from the amino acid pool to collagen suf-... 

Graney, R.L. and J.P. Giesy, Jr. 1986. Effects of long-term exposure to pentachlorophenol on the free amino acid pool and energy reserves of the freshwater amphipod Gammarus pseudolimnaeus Bousfield (Crustacea, Amphipoda). Ecotoxicol. Environ. Safety 12 233-251. 

MacdowalP found that tobacco leaves were most susceptible to injury by ozone (at 0.035 ppm for 5 h) just after full leaf expansion. This point corresponded to the banning of the decline in protein content. Lee modified the nitn en content of tobacco leaves by supplying urea and found a positive correlation of injury caused by ozone (at 1 ppm for 5 h) with nonprotein nitrogen, but not with protein. This result is in contrast with that of Ting and Mukeiji, who found that, in cotton leaves (in which the period of maximal susceptibility was at about 75% of full leaf expansion), the amino acid pool was low at the time of maximal susceptibility. However, ozone treatment (0.7 ppm for 1 h) increased the free amino acid pool. 

There are four sources of amino acids that enter the free amino acid pool in the body proteins in food proteins secreted into the stomach and intestine by the digestive glands endogenous proteins and microorganisms that die and release their protein in the colon. 

Asterobactin from Nocardia asteroides 257) contains salicylic, 2,3-dihydroxy-propionic, and 2-methyl-3-hydroxyundecanoic acid as well as derivatized Om and Arg residues (Fig. 4, 15). It forms a Fe " complex. The stereochemistry of the various centers was not determined but L-configuration is proposed for Om and Arg for biosynthetic reasons (general amino acid pool) and a negative of asterobactin. Whether the three compounds are involved in metal transport has not been investigated. 

The tightly regulated pathway specifying aromatic amino acid biosynthesis within the plastid compartment implies maintenance of an amino acid pool to mediate regulation. Thus, we have concluded that loss to the cytoplasm of aromatic amino acids synthesized in the chloroplast compartment is unlikely (13). Yet a source of aromatic amino acids is needed in the cytosol to support protein synthesis. Furthermore, since the enzyme systems of the general phenylpropanoid pathway and its specialized branches of secondary metabolism are located in the cytosol (17), aromatic amino acids (especially L-phenylalanine) are also required in the cytosol as initial substrates for secondary metabolism. The simplest possibility would be that a second, complete pathway of aromatic amino acid biosynthesis exists in the cytosol. Ample precedent has been established for duplicate, major biochemical pathways (glycolysis and oxidative pentose phosphate cycle) of higher plants that are separated from one another in the plastid and cytosolic compartments (18). Evidence to support the hypothesis for a cytosolic pathway (1,13) and the various approaches underway to prove or disprove the dual-pathway hypothesis are summarized in this paper. 

After centrifugation of the TCA/acetone extract, nonquenching aliquots of the supernatant were counted by liquid scintillation, and the pellet digested overnight in 2N NaOH. Counts present in the TCA/acetone supernatant were taken to represent the uptake of label into the soluble amino acid pool, while solubilized counts present in the NaOH digest were taken to represent incorporation into TCA-insoluble protein. 

Anno acid catabolism is part of the larger process of whole body nitro gan metabolism. Nitrogen enters the body in a variety of compounds present in food, the most important being amino acids contained in detary protein. Nitrogen leaves the body as urea, ammonia, and other products derived from amino acid metabolism. The role of body proteins in these transformations involves two important concepts the amino acid pool and protein turnover. 

The amino acid pool is defined as all the free amino acids in cells and extracellular fluid. 

A Golan-Goldhirsch, AM Hogg, FW Wolfe. Gas chromatographic analysis of the free amino acid pool of the potato and gas chromatography-mass spectrometry identification of y-aminobutyric acid and ornithine. J Agric Food Chem 30 320-323, 1982. 

Non-essential amino acids are L-Alanine, L-Arginine, Aspartic Acid, Glutamic Acid, L-Cystine, L-Glycine, L-Histidine, L-Proline, L-Serine, L-Tyrosine, and L-Glutamine. Non-essential amino acids can be made from other in the body s amino acid pool. 

I had a client whom thought Anadrol-50 was candy. He had damaged his liver enzymic process to a point where synthesis of Glutamine was quite poor. Since Glutamine makes up 50-70% of total muscle amino acid pools, and is used to repair and replace the stomach lining every few days, growth stopped. 

As can be deduced from Table 1.3, enrichment of the amino-acid pool by adding L-threonine or L-valine raises considerably the total cyclosporin production, accompanied by increased yields of cyclosporin C and cyclosporin D,... 

Whole-body distribution studies are essential for classical small-molecule drugs in order to exclude any tissue accumulation of potentially toxic metabolites. This problem does not exist for protein drugs, where the catabolic degradation products (amino acids) are recycled in the endogenous amino acid pool. Therefore, biodistribution studies for peptides and proteins are performed primarily to assess targeting to specific tissues as well as to identify the major ehmination organs [4]. 

In general, peptides and protein drugs are almost exclusively eliminated by metabolism via the same catabolic pathways as endogenous or dietary proteins, resulting in amino acids that are reutilized in the endogenous amino acid pool for de-novo biosynthesis of structural or functional body proteins. This has, for example,... 

Aside from gastrointestinal and renal metabolism, the liver may also contribute substantially to the metabolism of peptide and protein drugs. Proteolysis usually starts with endopeptidases that attack in the middle part of the protein, and the resulting oligopeptides are then further degraded by exopeptidases. The ultimate metabolites of proteins, amino acids and dipeptides, are finally reutilized in the endogenous amino acid pool. The rate of hepatic metabolism is largely dependent on specific amino acid sequences in the protein. 

A central feature of protein metabolism is the amino acid pool, consisting of amino acids in the bloodstream. Figure 4.5 illustrates the metabolic relationship of the amino acid pool to protein breakdown, synthesis, and storage. 

Proteins are synthesized from amino acids in the amino acid pool as discussed in Section 3.3. This occurs through the joining of H3N+- and -C02 groups at peptide bonds, with the elimination of H20 for each peptide bond formed. The body can make many of the amino acids it needs, but eight of them, the essential amino acids, cannot be synthesized in the human body and must be included in the diet. 

What is the amino acid pool What purposes does it serve ... 

Transfer RNA (tRNA) transports the required amino acids from the cell s amino acid pool to the ribosome. Each type of amino acid can only be transported by its own specific tRNA molecule. The tRNA, together with its amino acid residue, binds to the mRNA already bound to the ribosome. It recognizes the point on the mRNA where it has to deliver its amino acid through the use of a consecutive sequence of three bases known as an anticodon, which is found on one of the loops of the tRNA (Figure 1.33(b)). This anticodon binds to the complementary codon of the mRNA. Consequently, the amino acids can only be delivered to specific points on the mRNA, which controls the order in which amino acid residues are added to the growing protein. This growth occurs from the N-terminal end of the protein. 

The decay of proteins and amino acids in phytoplankton cultures, under oxic and anoxic conditions, indicated very little selectivity (Nguyen and Harvey, 1997). However, 15 to 95% of the total particulate amino acid pool consisted of polypeptides/proteins in anoxic treatments versus 8 to 65% in oxic conditions. The similarity of particulate amino acid composition during phytoplankton decay agrees with other work in the Delaware Bay estuary (USA), which showed similar composition in the dissolved combined amino acid (DCAA) pool (Keil and Kirchman, 1993). 

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