The Isolation, Purification And Structural Characterization Of Low Molecular Polysaccharide Purified From Radix Astragali

Radix astragali, the dried root of Astragalus memranaceus (Fisch.) Bge. or Astragalus membranaceus var.Mongholicus (Bge.) Hsiao,was known as a traditional Chinese herb.Ma-ny reports on the biological activities indicate that it possesses many biological functions in-cluding hepatoprotective, antioxidative, antiviral, antihypertensive, and immunostimulant pr-operties and can strengthen the superfacial resistance, discharge of pus and the growth of new tissues. The known constituents most associated with these properties are isoflavonoids,trite-rpene saponins, polysacccharides,γ-aminobutyricacid (GABA) and various trace elements. APS (Astragalus polysaccharides) is the main bioactive component among these constituents. The privous study in our lab showed that a purified low molecular weight APS (LMw-APS) has a significant immunobiological activity. So analyzing the structure of LMw-APS can provide more theoretical basis for the development of APS.This paper presents that a water-soluble polysaccharide isolated with hot water from Astragalus. After frozen, trawed and removed protain the crude polysaccharide was purified by Sepharose CL-6B gel filtration chromatography, and then we got the LMw-APS. HPLC indicated that LMw-APS (Mw=5600) was a homogeneous polysaccharide. The structural characterization of the purified LMw-APS was evaluated in this paper. Gas chromatography (G.C.) Analysis showed that LMw-APS is an acid heteropolysaccharide composing of Glc, Gal, Ara, GalA, Xyl, the molar ratio is 10:1.3:1.7:0.95:1.The structural characteristics of LMw-APS were investigated by methylation analysis, CMC-esterification-reduction, periodate oxidation, Smith degradation, partial acid hydrolysis and IR analysis. It has a backbone composed of (1→4)-linked Glc, (1→2)-linked Xyl and (1→3)-linked GalA with branches composed of (1→4)-linked Glc, (1→5)-linked Ara, (1→6)-linked Glc and terminated with Glc.