PubMed · 15045758
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Stephen J Freeland, Laurence D Hurst. 2004. Evolution encoded.. https://doi.org/10.1038/scientificamerican0404-84
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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.
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.
The DOSY analysis of dilute mixtures can be a challenge because a high signal-to-noise ratio is required for the best DOSY results. The sensitivity increase gained from new probe technologies (e.g. cold and nano probes) could enable one to acquire good DOSY spectra on sample amounts too low for conventional probes. In this article, we investigated the performance of cold and nano probes for qualitative DOSY analysis of concentrated and sample-limited mixtures, and compared the results with those of the conventional probe. We first measured the fluid flow for each probe. All three probes exhibited only relatively small levels of flow; consequently, a double-stimulated echo pulse sequence was not employed in the subsequent DOSY experiments. This decision was based on three facts: (1) flow-induced phase distortions were not observed, (2) our intentions are only to perform qualitative mixture analysis, and (3) discarding 50% of the already limited signal cannot be afforded. Although the cold and nano probes produced DOSY results for the concentrated mixture that were inferior to the conventional probe, the increase in the signal-to-noise ratio observed with these probes proved to be advantageous for the dilute three-component mixture. Furthermore, the cold probe showed slightly superior performance over the nano probe; thus, we conclude that among the probes examined the cold probe is best suited for qualitative DOSY analysis of sample-limited mixtures.