Stabilization of sialic acids in N-linked oligosaccharides and gangliosides for analysis by positive ion matrix-assisted laser desorption/ionization mass spectrometry.
Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry of oligosaccharides and gangliosides normally causes loss of sialic acid, particularly when alpha-cyano-4-hydroxycinnamic acid is used as the matrix. In addition, the potential signal is split because both positive and, to a greater extent, negative ions are formed while signals are frequently complicated as the result of partial alkali-salt formation. In order to stabilize the sialic acid moieties under MALDI conditions and to divert all of the signal into the positive-ion mode, a method involving their conversion into methyl esters has been developed. The method is relatively rapid and produces strong positive-ion signals from N-linked oligosaccharides containing sialic acid and from gangliosides. The latter compounds are stable, even in the presence of alpha-cyano-4-hydroxycinnamic acid. They give abundant molecular (MNa+) ions, but with sufficient residual in-source fragmentation to allow the sequence of the sugar chain to be determined. The sialic acid residue is stable after methylation, irrespective of its linkage to the parent molecule.
Powell
A K
AK
Oxford Glycobiology Institute, Department of Biochemistry, UK.
Harvey
D J
DJ
D000818:Animals; D002240:Carbohydrate Sequence; D002417:Cattle; D005732:Gangliosides / Q000032:analysis / Q000737:chemistry*; D008745:Methylation; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000032:analysis / Q000737:chemistry*; D012794:Sialic Acids / Q000032:analysis / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D000509:alpha-Fetoproteins / Q000032:analysis
D005732:Gangliosides; D009844:Oligosaccharides; D012794:Sialic Acids; D000509:alpha-Fetoproteins