Purification and biochemical characterization of a specific alpha-glucosidase from the digestive fluid of larvae of the palm weevil, Rhynchophorus palmarum L.

Abstract

A alpha-glucosidase was purified from the digestive fluid of the palm weevil Rhynchophorus palmarum L. (Coleoptera: Curculionidae) by chromatography on anion-exchange, gel filtration, and hydrophobic interaction columns. The preparation was shown to be homogeneous on polyacrylamide gels. alpha-glucosidase is a monomeric protein with a molecular weight of 60.60 kDa based on its mobility in SDS-PAGE and 61.05 kDa based on gel filtration. Maximal alpha-glucosidase activity occurred at 45°C and pH 5.6. The purified alphaglucosidase was stable at 37°C and its pH stability was in the range of 4.0–5.6. The enzyme readily hydrolysed pnitrophenyl-α-D-glucoside, maltose, maltodextrins and required strictly alpha-gluco configuration for activity. It cleaved glucose-glucose alpha-(1–2) linkages better than alpha-(1–4), alpha-(1–1), alpha-(1–3) and β-(1–6) linkages. The catalytic efficiency (Vmax/KM) values for p-nitrophenyl-α-D-glucoside, maltose, maltotriose, maltotetraose, maltopentose, maltohexose, Saccharose and Kojibiose were respectively 474.00, 36.81, 45.79, 45.85, 31.15, 6.63, 184.61 and 109.17. Alpha-glucosidase was capable of catalysing transglucosylation reactions. The yields in transglucosylation reactions at 37 °C were very high and could attain 62% with2-phenylethanol as glucosyl acceptors. This alpha-glucosidasehydrolyzed the products formed. It seems that the products formed were the phenylethyl-α-D-glucoside. These results suggest that alpha-glucosidase from the digestive fluid of the palm weevil Rhynchophorus palmarum is an exoglucosidase which catalyse the splitting of the α-glucosyl residue from the non reducing terminal of the substrate to liberate α-glucose.