Isolation and identification of a novel polysaccharide–peptide complex with antioxidant, anti-proliferative and hypoglycaemic activities from the abalone mushroom

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 (Fourier-transform 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.