Coexistence of Agaroid and Carrageenan Structures in a Polysaccharide from the Red Seaweed Rhodomela larix (Turner) C. Ag.

Abstract

A mixture of water-soluble sulfated polysaccharides from the red seaweed Rhodomela larix (Turner) C. Ag. was fractionated into two fractions, PS1 and PS2, in terms of differences in solubility of their cetylpyridinium salts in potassium chloride solution. The main fraction, PS2, consisted of D-galactose (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 identification of disaccharide derivatives arising from agaroid-type repeating units, [→3)β-D-Gal(1→4)L-AnGal(1→] and [→3)β-D-Gal(1→4)2-O-methyl-L-AnGal(1→]. Furthermore, occurrence of both agaroid- and carrageenan-type repeats, [→3)β-D-Gal(1→4)α-L-Gal(1→] and [→3)β-D-Gal(1→4)α-D-Gal(1→], was discovered by analyses of the methanol-insoluble material remaining after the partial methanolysis. Sulfate groups in PS2 appeared to be located at O-6 of the (1→4)-linked L- and 2-O-methyl-L-Gal residues, 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.