Coexistence of agaroid and carrageenan structures in a polysaccharide fromthe red seaweed Rhodomela larix (Turner) C. Ag.

A mixture of water-soluble sulfated polysaccharides from the red seaweed Rh odomela larix (Turner) C. Ag. was fractionated into two fractions, PS1 and PS2, in terms of differences in solubility of their cetylpyridinium salts i n potassium chloride solution. The main fraction, PS2, consisted of D-galac tose (Gal), 3,6-anhydro-L-galactose (L-AnGal), 2-O-methyl-L-AnGal, sulfate and small amounts of L-Gal, 2-O-methyl-L-Gal and D-xylose. Analysis of the methanol-soluble partial methanolysis product from PS2 led to identificatio n of disaccharide derivatives arising from agaroid-type repeating units, [- ->3)P-D-Gal(1-->4)L-AnGal(1-->] and [-->3)beta-D-Gal(1-->4)2-O-methyl-L-AnG al( 1-->]. Furthermore, occurrence of both agaroid- and carrageenan-type re peats, [-->3)beta-D-Gal(1-->4)alpha-L-Gal(1-->] and [-->3)beta-D-Gal(1-->4) alpha-D-Gal( 1-->], was discovered by analyses of the methanol-insoluble ma terial remaining after the partial methanolysis. Sulfate groups in PS2 appe ared to be located at O-6 of the (1-->4)-linked L- and 2-O-methyl-L-Gal res idues, O-6 of the (1-->3)-linked D-Gal residue, O-2 of the (1-->4)-linked L -AnGal residue and O-3 of (1-->4)-linked D-Gal residue.