STRUCTURAL INVESTIGATIONS OF GLUCANS FROM CULTURES OF GLOMERELLA-CINGULATA SPAULDING AND VONSCHRENCK

Methylation analysis, enzymic digestion, n.m.r. spectroscopy, and Smith degradation showed that the major extracellular polysaccharide, isolated from cultures of the fungus Glomerella cingulata, was a (1 --> 3)-beta-D-glucan with side chains of 1-4 (1 --> 3)-linked beta-D-glucose residues attached to position 6. A (1 --> 6)-beta-D-glucan was produced by the fungus in small proportions. Treatment of the (1 --> 3,1 --> 6)-beta-D-glucan (890 315) with > 0.05M NaOH at > 150-degrees, or Me2SO-H2O with a concentration of dimethyl sulfoxide of > 80%, irreversibly destroyed the highly ordered structure responsible for the high viscosity of aqueous solutions. The strong shift of the lambda-max of aqueous solutions of Congo Red by the degraded glucan, the fact that the mol. wt. of the original glucan was approximately 4 times higher than that of the degraded polymer, and the suppression of the n.m.r. signals for C-3 indicated that the original glucan had a highly ordered structure, probably built up from single helices.