title: Electrospray tandem mass spectrometric studies of phosphopeptides and phosphopeptide analogues.
abstract: A set of synthetic phosphopeptides and phosphopeptide analogues was studied by tandem nano-electrospray mass spectrometry. The influence of the collision offset and of the charge state of the molecular ion on phosphate-specific fragmentation processes was investigated in detail. H--D exchange experiments and structural considerations support a six-centered transition being present in the neutral loss of H3PO4 from serine, threonine and homoserine phosphopeptides, where the C-alpha hydrogen of serine or threonine or the C-beta hydrogen of homoserine is transferred to the protonated phosphate group. Neutral loss of H3PO4 at moderate collision offset potential represents a very abundant fragmentation process for serine, threonine and homoserine phosphopeptides. The most specific feature for discrimination of these phosphopeptides from tyrosine phosphopeptides is the m/z 79:97 ratio in the negative ion product spectra, which is consistently elevated in tyrosine phosphopeptides as compared with serine, threonine and homoserine phosphopeptides. The fragment ions of methylphosphono- and H-phosphonopeptides can be explained by the same mechanisms as are applicable to phosphopeptides.
authors.affiliation: Department of Pathochemistry, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Tholey
authors.forename: J
authors.initials: J
authors.lastname: Reed
authors.forename: W D
authors.initials: WD
authors.lastname: Lehmann
mesh_terms: D003903:Deuterium; D009842:Oligopeptides / Q000737:chemistry* / Q000302:isolation & purification; D010755:Organophosphates / Q000737:chemistry; D063065:Organophosphonates / Q000737:chemistry; D010748:Phosphopeptides / Q000737:chemistry* / Q000302:isolation & purification; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D009842:Oligopeptides; D010755:Organophosphates; D063065:Organophosphonates; D010748:Phosphopeptides; C037642:kemptide; D003903:Deuterium