Impact of D2O on the peptidization of L-alanine

Impact of D2O on peptidization of L-histidine

This is our sixth consecutive study carried out in an order to collect an experimental evidence on the impact of heavy water (D2O) on spontaneous peptidization of the proteinogenic α-amino acids and this time it is L-histidine (L-His). Scientists have not yet achieved a full consensus regarding the source of this very important amino acid in human and mammalian tissues, and on this particular question rather contradictory answers in form of experimental results are produced, equally supporting its exogenous and endogenous origin. Although this issue still remains unsolved, for practical demands of life sciences the two UN agencies, FAO and WHO, have both tentatively accepted that L-His is an exogenous α-amino acid. As analytical techniques, in our studies we employed high-performance liquid chromatography with the diode array detection (HPLC–DAD), mass spectrometry (MS), and scanning electron microscopy (SEM). Spontaneous peptidization of L-His dissolved in methanol + H2O, 7:3 (v/v) was carried out at 22 ± 0.5 °C in the darkness for a relatively long period of 314 h, and its progress was chromatographically checked by targeting concentration of the L-His monomer in the 12-min intervals. This investigation revealed alternating yet non-periodic concentration changes, indicating changeable formation and hydrolytic decay of the L-His-derived oligopeptides in the function of time, and a fast net concentration fall of the L-His monomer (witnessing to quite vigorous peptidization). Moreover, the MS results confirmed formation of the relatively high oligopeptides, falling within the range of two or more dozen L-His monomer units. Impact of D2O on peptidization of L-His was traced with use of MS and SEM for the L-His samples dissolved in aqueous methanol solvents containing 5, 10, 20, and 30% D2O, and also in pure D2O. Similar to the results earlier presented for five other proteinogenic α-amino acids, heavy water exerts a powerful inhibitory effect on spontaneous peptidization of L-His, equally perceptible when assessed with aid of mass spectrometry (with the mass spectra in the first instance playing the role of quasi-quantitative fingerprints), and based on purely qualitative micrographs derived with use of SEM.

The Hampering Effect of Heavy Water (D2O) on Oscillatory Peptidization of Selected Proteinogenic α-Amino Acids

We present an overview of our studies on the hampering effect of heavy water (D₂O) on spontaneous oscillatory peptidization of selected proteinogenic α-amino acids. The investigated set of compounds included three endogenous and two exogenous species. The experiments were carried out with use of high-performance liquid chromatography (HPLC), mass spectrometry (MS) and scanning electron microscopy (SEM). These techniques were chosen to demonstrate spontaneous oscillatory peptidization of α-amino acids in an absence of D₂O (HPLC) and the hampering effect of D₂O on peptidization (HPLC, MS and SEM). The HPLC analyses were carried out at 21 ± 0.5°C with each α-amino acid freshly dissolved in the binary liquid mixture of organic solvent + H₂O, 70:30 (v/v) or in pure D₂O for several dozen hours or several hours, respectively. The analyses with use of MS and SEM were carried out, respectively, after 7 days and 1 month of sample storage period in the darkness at 21 ± 0.5°C and for these experiments, each α-amino acid was dissolved in the liquid mixture of organic solvent + X, 70:30 (v/v), where X: H₂O + D₂O in volume proportions from 30:0 to 0:30. The results obtained with use of HPLC, MS and SEM point out to the strong hampering effect of D₂O on the oscillations and peptidization yields, yet the dynamics of these processes significantly depends on chemical structure of a given α-amino acid.