ABSTRACT
Objective: To isolate the Guiqi (Angelicae Sinensis Radix and Astragali Radix) polysaccharides (AAP) and study the structural characterization of AAP-2A. Methods: Hot water extracting and ethanol precipitating method was employed to isolate the AAP. A new fraction (AAP-2A) of AAP was obtained after AAP was purified by deproteination, gel chromatography on DEAE-52 cellulose, gel chromatography on Sephadex G-100, and other means. Sugar content of AAP-2A was determined using phenol sulfuric acid method. Chromatography techniques were used to determine the ultraviolet properties, infrared properties, relative molecular weight, absolute molecular weight, molecular conformation and molecular weight distribution, and monosaccharide composition with the molar ratio of AAP-2A. The connection, main chain and branched-chain structures, and the condition of branching point were studied by methylation and NMR methods. Results: The total sugar content of AAP-2A, which was absent of proteins and nucleic acids, was 98.98%. Infrared spectroscopy showed that AAP-2A had the typical signals of polysaccharides. The relative and absolute molecular weights of AAP-2A were above 6.68 × 105 and 2.252 × 106; AAP-2A was a neutral sugar and composed of rhamnose (Rha), galactose (Gal), arabinose (Ara), and glucose (Glc) with a molar ratio of 1 : 2.13 : 3.22 : 6.18. AAP-2A proved to be a heteropolysaccharide, with 1, 3-α-L-Rha, 1,3-β-D-Gal, 1,3-, 1,5-, and 1,3,5-α-L-Ara, 1,4- and 1,4,6-α-D-Glc residues in backbone and 1-α-D-Glcp residues in branches. Conclusion: AAP-2A is a new neutral heteropolysaccharide from Guiqi polysaccharides with a highly branched conformation.