Abstract: A pectic polysaccharide SJB was obtained from the alkali extract of mulberry leaves by DEAE-cellulose and gel filtration chromatography. The structures of SJB were identified on the basis of chemical methods(sugar component analysis, methylation analysis, partial acid hydrolysis) and spectral method(IR, ESI-MS, NMR). The results show that SJB with a molecular mass of 5.4×10⁴ consisted of rhammose, arabinose, glucose, galactose and galacturonic acid units in the molar ratio of 1.00∶1.26∶0.66∶2.04∶0.95. The main chain of SJB includes 1,2-linked, 1,2,4-linked Rhap and 1,4-linked, 1,3,4-linked GalAp. The side chains are mainly attached to the O4 of Rhap residues and O3 of GalAp residues, including terminal, 1,5-linked, 1,3,5-linked Araf and terminal, 1,4-linked Glcp, and terminal, 1,4-, 1,3-, 1,6-linked Galp. SJB is a new acidic polysaccharide for the first time isolated from Muberry leaves. The study of the effect of lowering blood glucose of SJB shows the inhibitory rate of SJB to PTP1B is 31.7% at the concentration of 20 μg/mL.

Key words: Mulberry leaves, Pectic polysaccharide, Structure analysis, Inhibitory activities of protein tyrosine phosphatase-1B