title: Some proline substituent effects in the tandem mass spectrum of protonated pentaalanine.
abstract: Tandem mass spectral effects of the replacement of alanine by proline in pentaalanine were studied. The principal difference when residue 3 or 4 is proline is the great enhancement of the y3 or y2 ion, respectively. This is precisely the principal difference which thermochemical arguments predict, since a y-type ion with N-terminal proline is estimated to be 32 kJ mol-1 more stable than with N-terminal alanine. When this proline effect and the effect of neutral diketopiperazine loss occur simultaneously, the y-type ion is not observed, as predicted from the additivity of substituent effects by the kinetic approach. No interpretation is offered for observations of b-type ion intensities, since the pattern is not obvious to us.
authors.affiliation: Department of Chemistry, University of North Carolina, Chapel Hill 27599-3290.
authors.forename: B L
authors.initials: BL
authors.lastname: Schwartz
authors.forename: M M
authors.initials: MM
authors.lastname: Bursey
mesh_terms: D000409:Alanine / Q000032:analysis*; D000595:Amino Acid Sequence; D008401:Gas Chromatography-Mass Spectrometry; D007700:Kinetics; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D011392:Proline / Q000032:analysis*
chemical_list: D011392:Proline; D000409:Alanine