Evaluation of glycosylation site heterogeneity and selective identification of glycopeptides in proteolytic digests of bovine α1‐acid glycoprotein by mass spectrometry

Glycosylation sites in bovine alpha 1-acid glycoprotein (AGP) have been identified, and the inherent heterogeneity evaluated, by capillary electrophoretic and reversed-phase liquid chromatography/electrospray-mass spectrometric analyses of proteolytic digests of this glycoprotein. The success of these methods in locating glycopeptides relied on significant heterogeneity within each glycosylation site. In order to rapidly locate sites in glycoproteins of any degree of heterogeneity, a novel mass spectrometric method was applied to selectively identify the glycopeptides in a proteolytic digest of bovine alpha 1-AGP. The glycopeptides were selectively located by the generation and detection of characteristic oxonium ions from the carbohydrate moieties by collision-induced dissociation (CID) during liquid chromatography/electrospray-tandem mass spectrometry, and liquid chromatography/CID mass spectrometry, in which fragmentation was induced in the supersonic expansion region of the electrospray source.