PubMed · 6449595
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R Imber, A Tsugita, M Wurtz, T Hohn. 1980-05-25. Outer surface protein of bacteriophage lambda.. https://doi.org/10.1016/0022-2836(80)90131-x
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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.
A model of amino acid (AA) uptake and metabolism by the mammary gland (udder) of a high producing dairy cow in mid-lactation is presented. Two cell types, milk-secreting alveolar epithelial cells, and constitutive stromal cells are represented separately. Solution of the model at steady state, with appropriate assumptions, allows calculation of amino acid (AA) pool sizes in tissue bound AA and milk protein bound AA, and concentrations of intracellular free AA. Bidirectional flux rates of amino acids between each of these pools is also estimated. The flow of two amino acids, phenylalanine (Phe) and tyrosine (Tyr), is described using uptake kinetics of the L-system AA transporter. Model results suggest that AA uptake capacity of the alveolar cells, and the amount/activity of protein translation components limit the rate of milk protein synthesis in the high-producing dairy cow. A considerable amount of experimental work is necessary to provide data, if a comprehensive quantitative understanding of milk protein synthesis is to be achieved.
Trimethylamine N-oxide (TMAO) is a solute concentrated in the urea-rich cells of elasmobranchs and coelacanth to offset the damaging effects of urea on intracellular protein structure and function. On the basis of transfer free energy measurements, favorable interaction of TMAO with amino acid side chains promote protein denaturation. This effect is more than offset by highly unfavorable TMAO-peptide backbone interactions that not only oppose denaturation but also provide stabilization against denaturation by urea. By combining transfer free energies of side chains and backbone with surface area exposure in the native and unfolded states of ribonuclease T1, the transfer free energies of native and unfolded protein from water to 1 M TMAO are estimated as 1.7 and 5.9 kcal/mol, respectively. These estimates agree favorably with the respective values of 1.2 and 5.4 kcal/mol determined experimentally by Lin and Timasheff [(1994) Biochemistry 33, 12695-12701]. The unfavorable transfer free energies of native and unfolded protein from water to TMAO provides a molecular level rationale for preferential hydration of proteins by osmolytes. Promotion of denaturation by urea is found to be offset by TMAO in a manner that is roughly additive of the combined effects of both solutes. The favorable interaction of urea with the backbone provides the dominant driving force for protein unfolding by this denaturant, and the unfavorable interaction of TMAO with backbone is the dominant force opposing urea denaturation. In solutions that contain significant organic solute concentration, the ascendance of the role of the peptide backbone over that of side chains can explain many observed effects in protein denaturation and stability induced by a variety of stabilizing and destabilizing organic solutes.