Phosphorylation of proteins is an essential signalling mechanism in eukaryotic and prokaryotic cells. Although N-phosphorylation of basic amino acid is known for its importance in biological systems, it is still poorly explored in terms of products and mechanisms. In the present study, two MS fragmentation methods, ECD (electron-capture dissociation) and CID (collision-induced dissociation), were tested as tools for analysis of N-phosphorylation of three model peptides, RKRSRAE, RKRARKE and PLSRTLSVAAKK. The peptides were phosphorylated by reaction with monopotassium phosphoramidate. The results were confirmed by 1H NMR and 31P NMR studies. The ECD method was found useful for the localization of phosphorylation sites in unstable lysine-phosphorylated peptides. Its main advantage is a significant reduction of the neutral losses related to the phosphoramidate moiety. Moreover, the results indicate that the ECD–MS may be useful for analysis of regioselectivity of the N-phosphorylation reaction. Stabilities of the obtained lysine-phosphorylated peptides under various conditions were also tested.

High-pressure denaturation of proteins can provide important information concerning their folding and function. These studies require expensive and complicated equipment. In this paper, we present a new convenient method for studying high-pressure denaturation of proteins combining DHX (deuterium-hydrogen exchange) and electrospray ionization MS. Application of various values of pressure causes different degrees of protein unfolding resulting in molecules with a different number of protons available for exchange with deuterons. After decompression a protein refolds and a certain number of deuterons are trapped within the hydrophobic core of a refolded protein. Redissolving the deuterated protein in an aqueous buffer initiates the DHX of amides located on the protein surface only, which can be monitored under atmospheric pressure by MS. Depending on the degree of deuteration after high-pressure treatment, the DHX kinetics are different and indicate how many deuterons were trapped in the protein after refolding. The dependence of this number on pressure gives information on the denaturation state of a protein. The distribution of deuterium along the sequence of a high-pressure-denatured protein was studied the ECD (electron-capture-induced dissociation) on a Fourier-transform mass spectrometer, enabling the monitoring of high-pressure denaturation with single amino acid resolution.