WATER-SOLUBLE RESERVE POLYSACCHARIDES FROM ACHLYA ARE (1-]3)-BETA-GLUCANS

The cytoplasmic water-soluble P-glucans of Achlya bisexualis are (1--> 3)-linked polysaccharides of two types: a small neutral and a large ph osphorylated. The carbon-13 nuclear magnetic resonance (NMR) spectrum of neutral glucan is consistent with a (1-->3)-beta-glucan with some ( 1-->6)-beta-linkages. Methylation analysis suggests a similar structur e, but also shows about 6% each of other linkages and other sugars. Ac id and enzyme hydrolysis data also support a moderately branched (1--> 3)-beta-glucan probably with single (1-->6)-beta-glucopyranosyl segmen ts. The data, however, do not exclude the possibility that the branche s are extended (1-->3)-linked residues. The molecular mass of neutral glucan is approximately 9000 with a dp of 50, when compared with algal laminaran by gel filtration chromatography. The carbon-13 NMR spectru m of phosphoglucan is qualitatively similar to that of neutral glucan. Aqueous hydrofluoric acid effectively cleaves phosphate from the phos phoglucan and produces a polymer of the size of neutral glucan. This m aterial is both qualitatively and quantitatively identical to neutral glucan in its carbon-13 NMR spectrum. The phosphorus-31 NMR spectrum o f the phosphoglucan reveals both mono- and diphosphoester linkages. We propose that the phosphodiester covalent bonds convert the smaller po lymer into the very large phosphoglucan.