Purification and characterisation of an intracellular enzyme with β-glucosidase and β-galactosidase activity from the thermophilic fungus Talaromyces thermophilus CBS 236.58

An intracellular β-glycoside hydrolase with β-glucosidase and β-galactosidase activity, designated β-glucosidase BGL1, was isolated to apparent homogeneity from the thermophilic ascomycete Talaromyces thermophilus CBS 236.58. The monomeric enzyme has a molecular mass of 50 kDa (SDS-PAGE) and an isoelectric point of 4.5–4.6. The enzyme is active with both glucosides such as cellobiose and galactosides including lactose; based on the catalytic efficiencies determined glucosides are the preferred substrates. β-Galactosidase activity of BGL1 is activated by various mono and divalent cations including Na+, K+ and Mg2+, and it is moderately inhibited by its reaction products glucose and galactose. Its pH optimum for the hydrolysis of galactosides is in the range of 5.5–6.0, and its optimum temperature was found to be 50 °C (15 min assay). In addition to its hydrolytic activity, BGL1 shows a significant transferase activity which results in the formation of galacto-oligosaccharides. These have recently attracted interest because of possible applications in food industry. The highest yields of oligosaccharides was approximately 20% when using 38 g l−1 lactose as the starting material.