Free Radical-Initiated Peptide Sequencing Mass Spectrometry for Phosphopeptide Post-translational Modification Analysis

다국어 초록 (Multilingual Abstract)

<P>Free radical-initiated peptide sequencing mass spectrometry (FRIPS MS) was employed to analyze a number of representative singly or doubly protonated phosphopeptides (phosphoserine and phosphotyrosine peptides) in positive ion mode. In contrast to collision-activated dissociation (CAD) results, a loss of a phosphate group occurred to a limited degree for both phosphoserine and phosphotyrosine peptides, and thus, localization of a phosphorylated site was readily achieved. Considering that FRIPS MS supplies a substantial amount of collisional energy to peptides, this result was quite unexpected because a labile phosphate group was conserved. Analysis of the resulting peptide fragments revealed the extensive production of <I>a</I>-, <I>c</I>-, <I>x</I>-, and <I>z</I>-type fragments (with some minor <I>b</I>- and <I>y</I>-type fragments), suggesting that radical-driven peptide fragmentation was the primary mechanism involved in the FRIPS MS of phosphopeptides. Results of this study clearly indicate that FRIPS MS is a promising tool for the characterization of post-translational modifications such as phosphorylation.</P>
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