Fast-atom-bombardment, negative-ion mass spectrometry of the mycobacterial O-methyl-D-glucose polysaccharide and lipopolysaccharides.

The mycobacterial O-methyl-D-glucose polysaccharide (MGP) and its acylated derivatives, the O-methyl-D-glucose lipopolysaccharides (MGLP), have been analyzed by fast-atom-bombardment mass spectrometry (F.a.b.m.s.). The molecular-ion peaks for MGP confirmed the degree of polymerization and, in addition, revealed a slight heterogeneity in the degree of methylation. Sequence ions were observed that are consistent with all known features of MGP structure. Spectra of the MGLP isomers confirmed the general distribution of the neutral and acidic acyl groups, and provided additional information regarding the specific location of individual acyl groups. The spectra of some MGLP preparations revealed that they were contaminated by lysophosphatidylinositol dimannoside. The study further documents the utility of F.a.b.m.s. for characterization of relatively large and complex carbohydrate derivatives.