Characterization of sulfoglycosphingolipids by direct probe electron impact mass spectrometry

Novel mono- and bis-sulfoglycolipids, monosulfogangliotriaosylceramide, bis-sulfogangliotriaosylceramide, and bis-sulfogangliotetraosylceramide, were recently isolated from rat kidney. These sulfoglycolipids and their partially- or fully-desulfated products were characterized by direct probe electron impact mass spectrometry as permethylated derivatives. The fragment ions obtained from permethylated-fully-desulfated-remethylated glycolipids included ions containing up to four monosaccharides plus C-1 and C-2 of acylated sphingoids as well as those plus C-1 to C-3 of acylated sphingoids. By the use of trideuteriomethyl iodide instead of methyl iodide in the remethylation step after desulfation, the sequences of the monosaccharides containing the sulfate ester were established. When the sulfate ester was present, the intensity of the ions derived from the carbohydrate moiety was much weaker in comparison to that of those from the permethylated-fully desulfated derivative. Instead, the intensity of the fragments from the ceramide moiety was very strong in the presence of the sulfate ester.