The polysaccharides from heterocyst and spore envelopes of a blue-green alga. Structure of the basic repeating unit.

The polysaccharides from the envelopes of heterocysts and spores of Anabaena cylindrica consist of repeating units containing 1 mannosyl and 3 glucosyl residues, all linked by beta(1 yields 3) glycosidic bonds, with glycosidic bonds, with glucose, xylose, galactose, and mannose present in side branches. Degradation of the polysaccharides with specific glycosidases has permitted identification of the linkages to almost all of the branches. When the polysaccharides, from which all but two types of side branches had been cleaved, were digested with a beta(1 yields 3) endoglucanase, glucose, a tri-, and a pentasaccharide were produced. The oligosaccharide products were identified as (see article of journal). The backbones of the polysaccharides were sequenced from the reducing terminus by a modified Smith degradation. Analysis with NaB3H4 at each stage of the degradation showed that the backbones terminate in the sequence Man-Glc-Glc-Glc and are therefore presumed to have the structure (Man-Glc-Glc-Glc)n, and that they contain an average of from 128 to 150 sugar residues. From the information obtained, the repeating sequences of the original polysaccharides from the two types of differentiated cells of A. cylindrica could be largely deduced and appeared to be identical.