Structural and physiological studies on the storage β-polyglucan of haptophyte Pleurochrysis haptonemofera
2008
The storage β-polyglucan and catabolic enzyme activities of the haptophyte Pleurochrysis haptonemofera were characterized. The storage β-polyglucan was prepared by the dimethylsulfoxide-extraction method. ¹³C- and ¹H-NMR spectroscopy revealed that the polyglucan consists of β-(1[rightward arrow]3)- and β-(1[rightward arrow]6)-linked glucose polymers, with a β-(1[rightward arrow]6)- to β-(1[rightward arrow]3)-linkage ratio of 1.5. Gel permeation chromatography showed that the molecular weight of the polyglucan is 1.1-8.4 x 10⁴ Da, with a peak at 3.4 x 10⁴ Da. The degree of polymerization, which was estimated from the amounts of total carbohydrate and reduced ends, was 203, corresponding to 3.3 x 10⁴ Da. A method for measurement of the β-polyglucan in a small amount of liquid culture involving a mixture of β-glucanases, Westase, was established. The β-polyglucan was localized in the soluble fraction of cells. The amount of β-polyglucan per cell increased at the stationary phase under continuous illumination and decreased in the dark, like those of storage α-polyglucans, starch of green algae and glycogen of cyanobacteria. The activities of β-1,3- and β-1,6-glucanases involved in the degradation of the storage β-polyglucan were assayed in vitro, both being optimal at pH 5.0. The β-1,3-glucanase activity, which was detected on active staining after native polyacrylamide gel electrophoresis, was partially purified by ammonium sulfate precipitation and anion exchange chromatography.
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