The polysaccharides from heterocyst and spore envelopes of a blue-green alga. Methylation analysis and structure of the backbones.

Lindberg's combined gas chromatography-mass spectrometry techniques for the analysis of partially methylated alditol acetate sugar derivatives were used to study the structures of polysaccharides from the envelopes of heterocysts and spores of Anabaena cylindrica. Polysaccharides from both envelopes are highly branched. Glucose, mannose, galactose, and xylose are at terminal positions, whereas glucose and mannose are at internal positions in these polymers. The molar percentages of the 11 partially methylated alditol acetate derivatives observed were approximately the same for both envelopes, suggesting that the envelope polysaccharides may be identical or almost identical. Smith degradation (periodate oxidation followed by reduction with sodium borohydride and mild acid hydrolysis) of the polysaccharides from the two kinds of envelopes removes the side branches without measurable fragmentation of the backbones. Gas chromatographic analysis of partially methylated alditol acetate derivatives of the sugars showed that the backbones of both envelope polysaccharides consist of glucose (Glc) and mannose (Man) linked by 1 leads to 3 glycosidic bonds. Disaccharides, trisaccharides, and tetrasaccharides obtained from the backbone polysaccharides by partial acid hydrolysis were fractionated by column chromatography and separated by high voltage paper electrophoresis. Analysis of these oligosaccharides established that the backbone polysaccharides from both heterocysts and spores consist of repetitions of the structural unit Glc leads to Glc leads to Glc leads to Glc leads to Man, and that all linkages in the backbones are in the beta configuration.