Study On The Molecular Structure Of Polysaccharede Of Cordyceps Militaris And Inhibitory Of ?-glucosidase Activity

Cordyceps militaris is a kind of medicine edible fungi, which has been used as Chinese medicinal materials in the treatment of disease for a long time. Polysaccharides were one of major and abundant bioactive constituents of Cordyceps militaris which had been confirmed by animal experiments in mice. But current research about structures of polysaccharide from Cordyceps militaris and its hypoglycemic activity are seldom reported.Therefore, the structures, the chemical modification, and a-glucosidase inhibitory activity of polysaccharide from Cordyceps militaris were studied in this article. The main research contents and results were given as follows:The Cordyceps militaris powder was extracted by hot water, and then the extract was deproteinized in papain-Sevage method, and crude polysaccharides were obtained by alcohol precipitation. The extraction rate was 6.78%. The crude polysaccharide was purified by chromatography on Sepheadex G-200 column to produce a kind of pure fractions termed CPS. The total sugar content of CPS was 95.83% tested by Phenol-sulfuric acid method. The average molecular weights of CPS was 1.15×10~3 kDa detected by HPGPC. The solution behavior of CPS were studied by congo red assay and circular dichroism spectra. The results showed that the solution pH, the metalion, DMSO and the complex would greatly increase the molecular asymmetry in solution.The polysaccharide CM-CPS was obtained by carboxymethylation modification of polysaccharide CPS. And the polysaccharide AC-CPS was obtained by acetylation modification. The specific rotation of CPS, CM-CPS and AC-CPS tested by polarimeter were +86°, +75° and +61°, respectively. I2-KI assay suggested that many branched chains attached to the backbone chain. The structure of CPS was studied by FT-IR and NMR and the result showed that CPS was composed of a-pyranose forms, CM-CPS and AC-CPS was modificated successful. Congo-red and CD test revealed that CPS existed triple-helical structure, and mainly in the form of random coil. The structure of CM-CPS and AC-CPS had changed, and the chains had been extended. The results of scanning electron microscope (SEM) and atomic force microscopy (AFM) showed that CPS, CM-CPS and AC-CPS had different appearance, which suggested that the structure of CPS had changed by modification. Differential scanning calorimetry (DSC) analysis showed similar thermal properties of 3 kinds of polysaccharides. The enthalpy change values of polysaccharides CM-CPS and AC-CPS were higher than that of CPS in the process of thermal degradation.The vitro ?-glucosidase inhibitory activities of CPS, CM-CPS and AC-CPS were determined, using the acarbose as a positive control. The experimental results showed that in a certain concentration range, the higher the concentration of CPS was, the higher the alpha glycosidase enzyme inhibition rate was. At the same concentration, the inhibition rate of polysaccharides under different solution conditions were changed and lower than the polysaccharide of Cordyceps militaris under the aqueous solution condition. And the inhibitory rate of CPS was higher than that of CM-CPS and AC-CPS. All of the above results showed that the advanced structure of polysaccharide had changed,and the a-glycosidase inhibitory activities also had changed.