Structural studies on the extracellular polysaccharide of the red alga, Porhyridium.

Partial acid hydrolyzates of the extracellular polysaccharide from Porphyridium cruentum yield three disaccharides and two uronic acids. These constitute all of the uronic acid in the polymer. The novel disaccharides are 3-O(alpha-D-glucopyranosyluronic acid)-L-galactose, 3-O-(2-O-methyl-alpha-D-glucopyranosyluronic acid)-D-galactose, and 3-O-(2-O-methly-alpha-D-glucopyranosyluronic acid)-D-glucose. The polyanion of high molecular weight contains D- and L-galactose, xylose, D-glucose, D-glucuronic acid and 2-O-methyl-D-glucuronic acid, and sulfate in molar ratio (relative to D-glucose) of 2.12:2.42:1.00:1.22:2.61. Preliminary periodate-oxidation studies suggest that the hexose and uronic acids are joined to other residues by (1 leads to 3) glycosidic linkages. About one-half of the xylose residues are (1 leads to 3)-linked.