The structure and biosynthesis of porphyran: a comparison of some samples

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Abstract
The water-soluble polysaccharides have been isolated and examined from about 40 different specimens of Porphyra spp. showing seasonal and environmental variations. There is a wide variability in the composi-tion of the polysaccharide extracts: 3,6-anhydro-L-galactose may be present in amounts from 5 to 19%; ester sulphate, 6-11%; 6-O-methyl-D-galactose, 3-28%; and galactose, 24-45%. Although the sulphate content is variable the ester always seems to occur predominantly as 1 [forward arrow]4-linked L-galactose 6-sulphate. Regularities in the analytical results suggest that 3,6-anhydro-L-galactose and L-galactose 6-sulphate are interchangeable between the polysaccharides, and that D-galactose and 6-O-methyl-D-galactose are related in a similar manner. In all the polysaccharides isolated, 3,6-anhydro-L-galactose and L-galactose 6-sulphate total approximately 1/2 of the sugar units, the other 1/2 being made up of D-galactose and 6-O-methyl-D-galactose. The implications of these and other aspects of the results for the homogeneity, structure and biosynthesis of porphyran are discussed. A preliminary attempt has been made to correlate polysaccharide composition with variation in the algal specimens examined.