PubMed · 14246262
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D G CATCHESIDE. 1964. INTERALLELIC COMPLEMENTATION.. https://pubmed.ncbi.nlm.nih.gov/14246262/
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Amino acid (AA) profiles from body fluids such as blood and urine are clinical indicators for diagnosing metabolic and hepatic diseases. Current quantitative methods, such as liquid chromatography-mass spectrometry (LC-MS) with isotopically labelled internal standards (ISs), are costly and technically demanding. This study proposes a cost-efficient alternative using structural isomers as ISs in a direct liquid infusion (DLI) tandem mass spectrometry (MS/MS) approach. The method leverages chimeric spectra and fragment intensity ratios to quantify AAs, demonstrating high linearity and precision even with a 3D ion trap mass analyser. This approach offers a viable strategy for AA quantification in preventive medicine, particularly for screening metabolic diseases such as phenylketonuria, diabetes, and liver dysfunction.
Amino acids, especially branched-chain amino acids such as l-leucine, have been shown to regulate activation of p70 S6 kinase and phosphorylation of 4E-BP1 through the mTOR signaling pathway. In our recent study, l-arginine was also shown to activate the mTOR signaling pathway in rat intestinal epithelial cells. l-Glutamine is an amino acid that is required for culturing of numerous cell types, including rat intestinal epithelial cells. In this study, we showed that l-glutamine inhibited the activation of p70 S6 kinase and phosphorylation of 4E-BP1 induced by arginine or leucine in rat intestinal epithelial cells. Although the molecular mechanism of l-glutamine-induced inhibition of the mTOR signaling pathway is still unknown, the presence of this novel signal pathway may indicate that individual amino acids play specific roles for cellular proliferation and growth.
For decades, the connection between cell size and division has been the subject of controversy. While in yeast, cell size checkpoints coordinate cellular growth with cell-cycle progression, it has been recently shown that large and small Schwann cells proliferate at the same rate (Conlon and Raff, 2003, J Biol 2:7). From this point of view, it is important to know whether normal and tumoral cells are similar. During continuous culture of NG108-15 neuroblastoma x glioma cells, the rate of proliferation, cell size, and external pH changed in parallel. At constant pH, the cell size-proliferation relationship followed a bell-shaped curve, so that proliferation was optimal within a cell volume window. In contrast, external acidification decreased proliferation independently of cell size. Using electrophysiological techniques, we showed that changes in cell size were dependent on both the uptake of nutrients and the passive influx of ions. Furthermore, an increase in cell size was associated with an increase in total proteins/cell. Another way to influence cell growth and proliferation is to alter the activity of the PI-3 kinase and target of rapamycin (TOR) signaling pathway. In NG108-15 cells, pharmacological inhibition of these proteins with LY 294002 and rapamycin respectively decreased proliferation but did not modify cell size. In contrast, aphidicolin treated cells did not proliferate, but they continued to increase in size. Altogether these results indicate that the proliferation of NG108-15 cells is controlled by both cell size-dependent and independent mechanisms that include extracellular pH and PI-3 kinase activity.