SULFATED GALACTANS FROM AUSTRALIAN SPECIMENS OF THE RED ALGA PHACELOCARPUS-PEPEROCARPOS (GIGARTINALES, RHODOPHYTA)

Polysaccharides from the red alga Phacelocarpos peperocarpos were extr acted with hot water, clarified, and precipitated with 2-propanol. The native preparation was highly sulfated (36.2% w/w). Alkali modificati on decreased the sulfate content by 2.0% w/w. The alkali-modified poly saccharide is composed mostly of galactose (Gal, 51 mol%) and 3,6-anhy drogalactose (AnGal, 41 mol%), with minor amounts of a mono-O-methylga lactose (MeGal, 1 mol%), xylose (Xyl, 6 mol%), and glucose (Glc, 1 mol %). The FTIR spectrum of the alkali-modified polysaccharide resembled K-carrageenan with absorption at 930 cm(-1) (indicative of AnGal) and 850 cm(-1) (Gal ii-sulfate). However, an additional, major band of abs orption occurred at 820 cm(-1) indicating the presence of equatorial s ulfate ester substitution at O-6 of Gal residues, A combination of lin kage and C-13 NMR spectroscopic analyses showed that the polysaccharid e was composed predominantly of a novel repeating-unit, O-beta-D-galac topyranosyl 4,6-disulfate)-(1 --> 4)-3,6-anhydro-alpha-D-galactopyrano se. Minor structural variations also occurred, including alternative p atterns of sulfation and the presence of terminal Xylp, The location o f the terminal Xylp residues was not certain but evidence supported th eir attachment at O-3 of some 4-linked Galp residues. The cell-wall ga lactans remain unchanged during the life cycle of the alga. (C) 1996 E lsevier Science Ltd.