Application of f.a.b.-m.s. to the products obtained from glycoconjugates upon periodate oxidation followed by borohydridc reduction and methylation gives the positions of binding of the monosaccharide residues on the basis of the sequences of the primary and secondary ions.
INTRODUClION
The introduction of f.a.b.-m.s. has provided new opportunities for analysing biological compounds which could not be dealt with by conventional e.i.-m.s. F.a.b.-m.s. can be used for derivatised and underivatised compounds in both positive and negative ion modes. Analysis of underivatised glycoconjugates gives information about the molecular weight and, after acetylation or methylation, the sequence of monosaccharides can be deduced. The positions of binding can sometimes be obtained after methylation, for example, the positions of substitution of a Zacetamido-Zdeoxy sugar unit can be determined by the secondary fragments formed after a primary cleavage of the 2-acetamido-2-deoxyhexosyl (HexNAc) linkagel. However, in general, the positions of binding cannot be determined by f.a.b.-m.s. We now describe a simple procedure for determining, from an f.a.b. mass spectrum, the positions of linkages between the monosaccharide residues in methylated oligosaccharides and glycosphingolipids.