title: First isolation and structural determination of cyclic beta-(1-->2)-glucans from an alga, Chlorella pyrenoidosa.
abstract: The aqueous extract of the edible green microalgae Chlorella pyrenoidosa is of interest because of its immunostimulatory activity. Some components in the extract have been identified previously, namely a unique type of arabinogalactan and a galactofuran. Further fractionation of this extract was accomplished by treating the aqueous solution of the fraction precipitated by addition of 1.5vol of 95% ethanol with cetyltrimethylammonium bromide. The residue obtained by concentration of the supernatant was fractionated further by anion-exchange chromatography and size-exclusion chromatography on Sephadex G-100. Two fractions from the latter column were retained, of which one was a starch-like alpha-(1-->4)-linked d-glucan with some alpha-(1-->6) branches, and the other contained a starch plus a mixture of beta-(1-->2)-d-glucans. ESI mass spectrometry was used to show that the mixture contained both cyclic and linear beta-(1-->2)-d-glucans in a cyclic:linear ratio of 64:36, based on intensities of mass spectral peaks. For the cyclic beta-(1-->2)-d-glucans, ring sizes ranged from 18 to 35 monosaccharides with the ring containing 21 glucose units (54% of the cyclic glucans) being greater than three times more abundant than the next most abundant component, the ring containing 22 glucose units (15%). No rings containing 20 glucose units were present. This is the first observation of cyclic beta-(1-->2)-d-glucans in algae, as far as we are aware. For the linear beta-(1-->2)-d-glucans, the component containing 20 glucoses was most abundant (35% of the linear glucans), while the component containing 21 glucose units was the next most abundant (17%). These relatively low-molecular-weight glucans had low immunostimulatory activity.
authors: Department of Chemistry, Dalhousie University, Halifax, NS, Canada B3H 4J3.
authors: Erick
authors: E
authors: Reyes Suárez
authors: Sarah M
authors: SM
authors: Bugden
authors: Fui Boon
authors: FB
authors: Kai
authors: Jaroslav A
authors: JA
authors: Kralovec
authors: Miguel D
authors: MD
authors: Noseda
authors: Colin J
authors: CJ
authors: Barrow
authors: T Bruce
authors: TB
authors: Grindley
mesh_terms: D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry; D002708:Chlorella / Q000378:metabolism*; D002852:Chromatography, Ion Exchange / Q000379:methods; D056890:Eukaryota / Q000378:metabolism*; D005663:Furans / Q000737:chemistry; D005690:Galactose / Q000737:chemistry; D005947:Glucose / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry / Q000379:methods; D008970:Molecular Weight; D009005:Monosaccharides / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D010504:Periodic Acid / Q000737:chemistry; D013347:Subcellular Fractions / Q000378:metabolism; D047071:beta-Glucans / Q000032:analysis / Q000737:chemistry* / Q000302:isolation & purification*
chemical_list: D002593:Cetrimonium Compounds; D005663:Furans; D009005:Monosaccharides; D047071:beta-Glucans; D010504:Periodic Acid; C009288:metaperiodate; D005947:Glucose; D010100:Oxygen; D005690:Galactose; D000077286:Cetrimonium