The extracellular polysaccharides of porphyridium cruentum and porphyridium aerugineum

The extracellular mucilages from Porphyridium cruentum and P. aerugineum contain D-xylose, D-glucose, D-and L-galactose, 3-O-methylxylose, 3- and 4-O-methyl-galactose, and D-glucoronic acid in the approximate molar proportions of 3:1:2.5:0.13:0.13:0.8 and 1.7:1:1.1:0.3:0.6:0.5, respectively. In addition, P cruentum mucilage contains 2-O-methylhexose (0.13) and 2-O-methylglucuronic acid (0.2), whereas P. aeruginum mucilage is devoid of these two sugars but contains 2,4-di-O-methylgalactose (0.5). Both polysaccharides contain ～10% of half-ester sulphate and appear to be linked to ～5% of protein. Attempted fractionation into homopolysaccharides was unsuccessful. Methylation, periodate oxidation, and partial hydrolysis studies revealed that the glucuronic acid is 1,3-linked and is attached solely to O–3 of D-galactose in both mucilages. The 2-O-methylglucuronic acid in P. cruentum is linked to O–4 of L-galactose. Xylose, glucose, and galactose are present in both mucilages as end groups, and 1,3- and 1,4-linked residues, with galactose and glucose also present as, 1,3,4-linked or sulphated residues. Molecular weight determinations on Sepharose 4B indicate a $\text{M}$_w of 4 x 10(su6) for P. cruentum mucilage and 5 x 10⁶ for that from P. aerugineum.