Linear beta-mannose-containing polysaccharide, beta-xylan, and amylose from the cultured photobiont Trebouxia sp. of the ascolichen Ramalina celastri.

The cultured photobiont Trebouxia sp. of Ramalina celastri was successively extracted at 100 degrees C with hot water, 2% aqueous KOH, and 10% aqueous KOH to give polysaccharide-containing fractions A (2.9%), B (3.9%), and C (0.9% yield) respectively. The intact biont contained 3.8% amylose, which was present in each fraction, and was identified by a blue color formed with iodine solution. In fraction A, and following retrogradation from aqueous solution, it was characterized by (13)C-NMR spectroscopy. Fraction B was treated with alpha-amylase to give a water-soluble fraction consisting mainly of beta-mannose-containing polysaccharides (1.5% yield), whose main component had dn/dc 0.162 and M(r) 17 kDa. Fraction C was subjected to freeze-thawing and the precipitate was treated with alpha-amylase to give a resistant, linear, low molecular mass (1-->4)-linked beta-xylan. The beta-D-mannopyranan preparation contained mainly of 3-O- (28%), 4-O- (11%), and 6-O-substituted Manp units (35%), with 3-O-substituted Rhap units (11%). A controlled Smith degradation provided a beta-mannan with nonreducing end- (8%), 3-O- (85%) and 6-O-substituted units, showing (1-->3)- and (1-->6)-linked structures in the original polysaccharide. These could be present as block-type structures.