An Exocellular Polysaccharide From the Diatom Gomphonema Olivaceum¹,²

SUMMARY An acidic polysaccharide produced by Gomphonema olivaceum was extracted with hot water after conversion to its potassium form. Recovered in 2–3% yield, the β‐linked polysaccharide was composed primarily of d ‐galactose, d ‐xylose, and an alkalistable sulfate ester in the ratio of 1:1:1.2. Several other minor components including a uronic acid were observed but not further identified. Periodate oxidation was complete in 40 hr at 4 C with the consumption of 0.88 mole of oxidant and production of 0.26 mole of acid per sugar residue. Half of the d ‐galactose in the polysaccharide was not oxidized by periodate: the remainder was cleaved between C 2 and C 3 . Of the d ‐oxylose residues, 35% were not oxidized; 15% were cleaved beetween C 2 and C 3 ; and 50%, presumbably a nonreducing side‐chain moiety, afforded formic acid. From these data two possible structures have been proposed.