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A novel antioxidant polysaccharide-peptide complex LB-1b from the fruiting bodies of the edible abalone mushroom (Pleurotus abalonus) was purified and identified. The structural characteristic of LB-1b was identified by FTIR (Fouriertransform IR), 13C NMR and 1H NMR spectroscopy. LB-1b is a polysaccharide-peptide complex that contains glucose, rhamnose, glucuronic acid and galactose in the molar ratio of 22.4:1:1.7:1.6 and the N-terminal sequence of its peptide moiety has also been determined. The N-terminal amino acid sequence of LB-1b, IPKERKEFQQAQHLK, showed some resemblance to antioxidant enzymes. LB-1b exhibited high antioxidant activity in erythrocyte haemolysis in vitro and the anti-proliferative activity towards hepatoma HepG2 cells and breast cancer MCF7 cells with an IC50 of 24 and 14 µM respectively. LB-1b also demonstrated hypoglycaemic activity in drug-induced diabetic mice and anti-HIV-1 RT (reverse transcriptase) with an IC50 value of 12.5 µM. [ABSTRACT FROM AUTHOR]