Water-soluble reserve polysaccharides from Achlya are (1 leads to 3)-beta-glucans

The cytoplasmic water-soluble β-glucans of Achlya bisexualis are (1→3)-linked polysaccharides of two types: a small neutral and a large phosphorylated. The carbon-13 nuclear magnetic resonance (NMR) spectrum of neutral glucan is consistent with a (1→3)-β-glucan with some (1→6)-β-linkages. Methylation analysis suggests a similar structure, but also shows about 6% each of other linkages and other sugars. Acid and enzyme hydrolysis data also support a moderately branched (1→3)-β-glucan probably with single (1→6)-β-glucopyranosyl segments. The data, however, do not exclude the possibility that the branches 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 spectrum of phosphoglucan is qualitatively similar to that of neutral glucan. Aqueous hydrofluoric acid effectively cleaves phosphate from the phosphoglucan and produces a polymer of the size of neutral glucan. This material is both qualitatively and quantitatively identical to neutral glucan in its carbon-13 NMR spectrum. The phosphorus-31 NMR spectrum of the phosphoglucan reveals both monoand diphosphoester linkages. We propose that the phosphodiester covalent bonds convert the smaller polymer into the very large phosphoglucan.