CELL-WALL POLYSACCHARIDES FROM AUSTRALIAN RED ALGAE OF THE FAMILY SOLIERIACEAE (GIGARTINALES, RHODOPHYTA) - HIGHLY METHYLATED CARRAGEENANS FROM THE GENUS RHABDONIA

The hot water-soluble polysaccharides from Rhabdonia coccinea and R. v erticillata were characterised by a combination of constituent sugar a nalysis, sulphate and pyruvate content assays, infrared (IR) spectrosc opy, linkage analysis, and C-13-nuclear magnetic resonance (NMR) spect roscopy. These revealed unique polysaccharides belonging to the red al gal galactan family. The polysaccharides had IR spectra resembling tha t of l-carrageenan, but were rich in 6-O-methylgalactose (ca. 31 mol% and 17 mol% for R. coccinea and R. verticillata, respectively). Data f rom C-13-NMR spectroscopy provided evidence that the polysaccharides w ere carrageenans rather than agarocolloids. The preparations contained mainly l-carrageenan, partially methylated at C(O)6 of the 3-linked g alactose residue. The polysaccharide from R. verticillata also contain ed significant quantities of 3-O-methylgalactose and pyruvate. The unu sual sugar 3-O-methylgalactose occurred primarily as main-chain 4-link ed residues, with a small proportion in the form of terminal residues. Other structural variations occurred in the polysaccharides of both s pecies.