Concurrence of agaroid and carrageenan chains in funoran from the red seaweed Gloiopeltis furcata post. et ruprecht (cryptonemiales, rhodophyta)

Abstract

Funoran extracted from the red seaweed Gloiopeltis furcata Post. et Ruprecht was fractionated into four polysaccharide fractions in terms of differences in solubility of their cetylpyridinium salt in potassium chloride solution. Besides the main fraction constructed by an agarose sulphate structure with negative optical rotation, minor polysaccharide fractions with positive optical rotation were obtained. One of the minor polysaccharide fractions contained d- and l-galactose (Gal), 6-O-methyl- d-Gal, 3,6-anhydro- l-Gal and sulphate. Partial hydrolysis and partial methanolysis studies of this fraction led to identification of oligosaccharides attributable to both agaroid and carrageenan backbones, i.e. [ → 3) d-Gal(1 → 4) l-Gal(1 → ][→ 3) d-Gal(1 → 4)3,6-and [ → 3)6- O-methyl- d-Gal(1 → 4)D-Gal(l → ]. Methylation analysis and alkaline treatment study of this fraction revealed that the sulphate groups were located at O-6 of all the (1 → 4)-linked l- and a part of the (1 → 4)-linked d-Gal residues, O-6 of a part of the (1 → 3)-linked d-Gal residue, and both O-2 and O-4 of the (1 → 3)-linked 6-O-methyl- d-Gal residue and the other (1 → 3)-linked d-Gal residue.