MALDI Mass Spectra of Protein Digests Before and After Enrichment on a Modified Plate
Prior to enrichment, the mass spectrum of a sample containing 3 digested phosphoproteins shows only minor signals from phosphopeptides (top spectrum). The large number of non-phosphorylated proteolytic peptides may suppress phosphopeptide signals. After enrichment using a MALDI plate coated with polymer-oxotitanium brushes, many phosphopeptide signals appear from all 3 of the proteins (bottom spectrum).
MALDI mass spectra of model protein digests without phosphopeptide enrichment (top) and after enrichment on MALDI plates modified with polymer-oxotitanium brushes (bottom). MS peaks labeled with α, β, and o represent phosphopeptides generated from α-casein, β-casein and ovalbumin, respectively, and red symbols denote multi-phosphorylated peptides. For more details see J. Proteome Res. 9, 3005–3015 (2010).