Carrageenan and agaran structures from the red seaweed Gymnogongrus tenuis

Abstract

The galactan system biosynthesized by the red seaweed Gymnogongrus tenuis (Phyllophoraceae) is con-stituted by major amounts of /-carrageenans, with predominance of -structures, which were isolatedby extraction with hot water in high yield (∼45%). A small amount of non-cyclized carrageenans mostlyof the -type was also obtained. Besides, 12% of these galactans are agaran structures, which were presentin major quantities in the room temperature water extracts, but they were also found in the hot waterextract. They are constituted by 3-linked -d-galactose units partially substituted on C-6 with sulfate orsingle stubs of -d-xylose and 4-linked residues that comprise -l-galactose units partially sulfated ormethoxylated on C-3 or sulfated on C-3 and C-6 and 3,6-anhydro--l-galactose. Related structural pat-terns were previously found for agarans synthesized by other carrageenophytes. Results presented hereshow that these agarans are low molecular weight molecules independent of the carrageenan structures,with strong interactions between them.