Water molecule assisted proton mobility in gaseous protonated GlyPro and ProGly

The thermal hydrogen/deuterium exchange behaviors of GlyProH(+), ProGlyH(+) , and ValGlyH(+) in the reactions with D2O have been studied in a Fourier t ransform ion cyclotron resonance mass spectrometer. The analyzed behaviors are consistent with our earlier conclusions that more basic N-terninal amin o acids lower the overall efficiency of the hydrogen atom exchange in proto nated alkyl dipeptides, It appears that the mobility of a proton over the b asic sites in peptides can be restricted drastically by N-terminal proline, relative to peptides with other N-terminal alkyl amino acids. (C) 2000 Els evier Science B.V.