SULFATED MUCIN OLIGOSACCHARIDES FROM PORCINE SMALL-INTESTINE ANALYZEDBY 4-SECTOR TANDEM MASS-SPECTROMETRY

The fraction of sulphated oligosaccharide alditols isolated from mucin glycopeptides of porcine small intestine 'insoluble' mucin complex wa s analysed by negative-ion fast atom bombardment (FAB) tandem mass spe ctrometry. Collision-induced dissociation (CID) tandem mass spectra of native and peracetylated species were compared with standards of sulp hated monosaccharides. The tandem mass spectra revealed structural inf ormation of the carbohydrate sequence and sulphate position. Negative- ion FAB ionization of the peracetylated sulphated oligosaccharide aldi tols was at least three times more sensitive than that of the native s ulphated oligosaccharide alditols, as revealed by comparing the signal -to-noise ratios, and allowed the detection of eleven compared with si x pseudomolecular ions. Fourteen structures were determined from the C ID tandem mass spectra obtained. The main sulphation site was Cd of an N-acetylglucosamine 6-linked to the N-acetylgalactosaminitol. C-3 of the N-acetylgalactosaminitol could be unsubstituted or extended with a series of up to three monosaccharide residues including blood group H determinants and blood group A determinants, Also, the sulphated N-ac etylglucosamine could be further extended. The most abundant structure was a monosulphated trisaccharide with the sequence Gal --> 3(SO3- -- > 6GlcNAc --> 6)GalNAcol. The sulphation at Cd of N-acetylglucosamine seems to be a common feature for O-linked oligosaccharides, and has be en described both for skeletal keratan sulphates and respiratory mucin oligosaccharides. Low-abundance ions were also detected from oligosac charides with sulphation at C-3 of an amino sugar residue. This seems to be a novel sulphation site for mucin oligosaccharides.