Oxidation products of S-Adenosyl methionine probed by IRMPD spectroscopy: unraveling the protective effects on oxidative stress

S-Adenosyl methionine (SAM) is a biomolecule containing an adenosyl cation bonded to the sulfur atom of methionine (Met). SAM is a primary methyl donor and the precursor of the Gluthatione (GSH). Due to the role played by SAM in the proper functioning of cellular metabolism, it is an interesting biomolecule to be investigated as a potential therapeutic agent for the treatment of various pathologies and disorders and in scavenging hydroxyl radicals. In this work, the oxidation process of SAM induced by gamma-radiolysis has been investigated by collision-induced dissociation tandem mass spectrometry (CID-MS2) and Infrared Multiple Photon Dissociation Spectroscopy (IRMPD) to reveal the modified sites and to characterize the 3D structure of the oxo-forms of SAM in the gas phase. Both CID-MS2 and IRMPD experiments coupled with DFT calculations revealed that only the adenine moiety of the molecule is oxidized, protecting the methionine from oxidation and preserving its function.