PubMed · 12977299
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R VORMANN, W RUMMEL. 1952. [Specific-dynamic effects in vitro].. https://pubmed.ncbi.nlm.nih.gov/12977299/
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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.
The mammalian target of rapamycin (mTOR) has been identified as a growth factor and nutrient-sensitive molecule that controls the translational machinery and cell growth. Rapamycin-sensitive (RS) signaling events have also been shown to be necessary for mechanical load-induced growth of skeletal muscle, but the mechanisms involved in the mechanical activation of RS signaling are not known. The finding that mechanical stimuli induce nutrient uptake in skeletal muscle raises the possibility that mechanically induced RS signaling is mediated via a nutrient-dependent mechanism. To investigate this hypothesis, skeletal muscles (ex vivo) were stimulated with nutrients or intermittent mechanical stretch and the phosphorylation of p70S6k [P-p70(389)], PKB [P-PKB], mTOR [P-mTOR(2481)], and p38 [P-p38] was assessed. In comparison to vehicle-treated controls, both nutrient and mechanical stimuli induced P-p70(389), neither stimulus altered P-PKB or P-mTOR(2481), and only mechanical stimuli induced P-p38. The nutrient and mechanically induced increase in P-p70(389) was blocked by rapamycin, but only nutrient-induced signaling to P-p70(389) was blocked by wortmannin. Furthermore, the mechanically induced increase in P-p70(389) was not impaired by the removal of exogenous nutrients. Taken together, these results indicate that exogenous nutrients are not required for mechanically induced RS signaling and that nutrient and mechanical stimuli activate RS signaling through distinct upstream mechanisms.
4-Amino-(D3)-trishomocubane-4-carboxylic acid is a constrained alpha-amino acid residue that exhibits promising conformational characteristics, i.e., helical and beta-turns. As part of the development of conformational guidelines for the design of peptides and protein surrogates, the conformational energy calculations on trishomocubane using molecular mechanics and ab initio methods are presented. The C(alpha) carbon of trishomocubane forms part of the cyclic structure, and consequently a peptidic environment was simulated with an acetyl group on its N-terminus and a methylamide group on its C-terminus. Ramachandran maps computed at the molecular mechanics level using the standard AMBER (parm94) force field libraries compared reasonably well with the corresponding maps computed at the Hartree Fock level, using the 6-31G* basis set. Trishomocubane peptide (Ac-Tris-NHMe) is characterized by four low energy conformers corresponding to the C7ax, C7eq, 3(10), and alpha(L) helical structures.