Where is amino acid pool

Cell Biol. Hu, A. In: Physarum polycephalum , object of research in cell biology A. Stuttgart: Fischer Acta , — In the growing plasmodium. In: Methods in cell biology D. Huffacker, R. Plant Physiol. Lowry, H. McCormick, J. Mohberg, J. Cell Res. Mortimore, G. Oxender, D. VI, Metabolic transport L. Hokin, ed. Amino acid transport in microorganisms, 3rd ed. Partridge, W. Poole, B.

Turnover of peroxisome proteins. Sauer, H. Wilhelm Roux' Arch. Schimke, R. Stegeman, W. Polypeptide products of mitochondrial transcription and translation in vivo as revealed by selective labeling with 3 H-leucine. Stegemann, H. Hoppe-Seyler's Z.

In the myocytes, the extracellular glycine enrichment was 5-fold higher than the intracellular enrichment, whereas phenylalanine differed little between extra- and intracellular enrichment.

There was also a significant gradient from extra- to intracellular enrichment of proline that probably reflects de novo synthesis of the amino acid.

Nonetheless, comparable values for FSR were attained with all tracers when intracellular amino acid enrichments were used. There are 2 important points related to our findings. First, the discrepancy between enrichment in the extra- and intracellular free pools of glycine was likely due to the dilution of the intracellular pool by de novo synthesized glycine, which does not occur in the case of phenylalanine.

Second, irrespective of differences in gradients between extra- and intracellular enrichment, the intracellular free enrichment accurately reflected the true precursor enrichment, regardless of the amino acid tracer.

Thus, the precursor tracer for measurement of FSR does not need to be an essential amino acid i. Theoretically, the individual amino acid tracer used should not affect the rate of synthesis calculation, irrespective of the composition of the protein produced. This was true in our present experiment, despite a wide range in the relative contribution to the final product. Collagen is the predominant protein produced by fibroblasts.

Collagen has a high abundance of both glycine and proline and a small proportion of phenylalanine. Nonetheless, all 3 tracers yielded the same protein FSR in this study. Because both glycine and proline can be synthesized within fibroblasts, their enrichment was markedly below the medium enrichment, yet the true precursor enrichment was accurately reflected by the intracellular enrichment. In vivo, the extracellular fluid compartment in skin is larger in relation to the intracellular fluid compartment than is the case in muscle.

However, these compartments are commonly pooled when in vivo samples are measured. Thus, the tissue free amino acid pool, which combines interstitial and intracellular fluid, is likely to be more reflective of interstitial fluid enrichment in skin than in muscle.

Further, the results of the current experiment indicate that the gradient from interstitial to intracellular enrichment for some amino acids, such as glycine, is larger for skin than it is for muscle. It is therefore not surprising that the tRNA enrichment in skin of individuals given [ 15 N]glycine was significantly lower than the tissue-free glycine enrichment 6.

Thus, if the tissue-free glycine enrichment is used as the precursor for protein synthesis, correction must be made for the contribution of the interstitial fluid glycine if an accurate estimate of precursor enrichment is to be obtained.

Further, if a different amino acid, such as phenylalanine, is used as tracer that has a much smaller gradient from blood to intracellular enrichment, then a different rate of skin protein synthesis would likely be obtained if uncorrected tissue-free enrichment was used as the precursor for synthesis. When these in vitro studies are interpreted in the context of the in vivo results, it is reasonable to conclude that the intracellular free amino acid pool generally reflects the true precursor for protein synthesis.

However, it may be that leucine represents a specific exception to that conclusion. Although the discrepancy shown in Ref. Thus, an in vitro study performed in cultured skeletal muscle cells by Schneible et al. Muscle cells were prelabeled with 14 C-leucine and then labeled medium was withdrawn and medium containing 3 H-leucine was added.

With this approach it was possible to distinguish the percentage of precursor derived from the medium for oxidation and for synthesis tRNA. The exact values were dependent on the leucine concentration in the medium, but at all concentrations tested most of the precursor for oxidation was derived from the medium, whereas most but not all of the leucine bound to tRNA was derived from the intracellular pool Thus, it is possible that leucine may be compartmentalized within the cell.

Even so, the results from the study of Schneible et al. Recycling of labeled amino acids from protein turnover and isotopic exchange from transamination reactions are potential problems in establishing isotopic steady state. However, the constant enrichments of protein bound amino acids during d 5 and 20 Figs. We performed the study once in each of the respective cell lines. Studies involving cell lines are typically not repeated because measurements are so reproducible.

Therefore, the differences in enrichment in the different pools reflect physiological differences rather than differences due to measurement error. The more pertinent question than statistical differences between precursors regards which value more closely reflects the true value. It is clear from Table 2 that in every case the intracellular free pool is reasonably close to the product plateau enrichment.

In contrast, this is not the case for the culture medium enrichment. This leads to the conclusion that the intracellular free amino acid pool accurately reflects the true precursor enrichment for protein synthesis. In summary, we validated intracellular free amino acid enrichment as surrogate for precursor enrichment for protein synthesis in cell culture.

In both fibroblasts and myocytes, protein synthesis rates calculated from intracellular free amino acid enrichments were close to the true values of protein synthesis, irrespective of the tracer.

Using extracellular amino acid enrichments resulted in underestimation of protein synthesis. This approach is applicable to in vivo studies in human subjects. Wolfe , R. Google Scholar. Google Preview. Carraro , F. Reeds , P. Baumann , P. El-Harake , W. Everett , A. Martin , A. McKee , E. Garlick , P. Smith , K. Zhang , X. Airhart , J. Stirewalt , W. Schneible , P.

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Views Total views. Actions Shares. No notes for slide. Amino acid pool 1. Amino Acids in Blood 6. Tissue AA: Tissue proteins 2. Plasma proteins formation 3. Formation of globin of Hb 4. Formation of Enzyme Proteins 5. Proteins of Milk 7. Other nitrogenous substances. Formation of glucose glucogenic AA 9.