Impact of D2O on the peptidization of l-methionine

This is our follow-up study carried out in an order to collect experimental evidence regarding the impact of heavy water (D2O) on the spontaneous oscillatory peptidization of the sulfur-containing proteinogenic α-amino acids and this time our target is l-methionine (l-Met). Our earlier study has been focused on l-cysteine (l-Cys) and it seemed interesting for us to compare the effect induced by D2O on these two structurally related compounds. In a broader sense though, our goal is to investigate if spontaneous oscillatory peptidization of various different proteinogenic α-amino acids might play any role in living organisms. As analytical techniques, we used high-performance liquid chromatography with the evaporative light-scattering detection (HPLC-ELSD), mass spectrometry (MS), scanning electron microscopy (SEM), and turbidimetry. The obtained results demonstrate that heavy water seriously hampers the oscillatory peptidization of l-Met, apparently due to the presence of the deuterium cation in the reaction medium and in the first instance, due to isotopic substitution of two functionalities participating in peptidization, i.e., –COOH and –NH2. This effect is fully analogous to that earlier reported for l-Cys. A cautious conclusion can be drawn that far more experimental evidence is still needed to be able to judge about an importance (or otherwise) of the oscillatory peptidization of proteinogenic α-amino acids for various different life processes.