HYDROGEN-DEUTERIUM EXCHANGE OF MASS-SELECTED PEPTIDE IONS WITH ND3 IN A TANDEM SECTOR MASS-SPECTROMETER

Hydrogen/deuterium exchange of mass-selected protonated peptide ions with ND3 is investigated in a four sector tandem mass spectrometer equipped with a high-pressure collision cell. The dependence of H/D exchange on the pressure of ND3, on collision energy and on proton affinities (PAs) of the peptides is examined. For leucine enkephalin, a peptide without strongly basic residues, the maximum number of H/D exchanges observed can correspond to the maximum number of active hydrogen atoms iii the ions. In peptides with basic residues such as arginine, the H/D exchange proceeds more slowly and more selectively. H/D exchange is observed for renin substrate whose PA is estimated to be higher than ND, by more than 50 kcal mol-1. The pattern of H/D exchange of leucine enkephalin shows discrepancy with the number of hydrogen atoms in the peptide ion expected to undergo fast H/D exchange, thus indicating possible conformational effects. When protonated leucine enkephalin is reacted with ND, under predominantly single-collision conditions, the incorporation of deuterium into fragment ions is found to vary, depending on the type of fragment ion. This differential incorporation of deuterium may be informative about the nature of the processes leading to the formation of fragment ions.