Carrageenan and agaran structures from the red seaweed Gymnogongrus tenuis

The galactan system biosynthesized by the red seaweed Gymnogongrus tenuis (Phyllophoraceae) is constituted by major amounts of kappa/iota-carrageenans, with predominance of iota-structures, which were isolated by extraction with hot water in high yield (similar to 45%). A small amount of non-cyclized carrageenans mostly of the v-type was also obtained. Besides, 12% of these galactans are agaran structures, which were present in major quantities in the room temperature water extracts, but they were also found in the hot water extract. They are constituted by 3-linked beta-D-galactose units partially substituted on C-6 with sulfate or single stubs of beta-D-xylose and 4-linked residues that comprise alpha-L-galactose units partially sulfated or methoxylated on C-3 or sulfated on C-3 and C-6 and 3,6-anhydro-alpha-L-galactose. Related structural patterns were previously found for agarans synthesized by other carrageenophytes. Results presented here show that these agarans are low molecular weight molecules independent of the carrageenan structures, with strong interactions between them. (C) 2015 Elsevier Ltd. All rights reserved.