Purification and characterization of two β-D-glucosidases from an Aspergillus niger enzyme preparation:: affinity and specificity toward glucosylated compounds characteristic of the processing of fruits

Two beta-D-glucosidases were purified to homogeneity from an Aspergillus niger enzyme preparation. Their respective molecular weights (118 kDa for beta-D-glucosidase A and 109 kDa for beta-D-glucosidase B) and pH and temperature properties were in the range of values reported for fungal beta-D-glucosidases. They were competitively inhibited by glucose, gluconolactone, and deoxynojirimycin. Their substrate specificities (specific activities, affinity and catalytic constants) were determined on three glucosylated compounds corresponding to the technological applications of beta-D-glucosidases in the processing of fruits; malvidin-3-glucoside (decolorization), geranyl-beta-D-glucoside (aroma enhancing), and cellobiose (cellulolysis); in comparison with the activity on p-nitrophenyl-beta-D-glucoside. beta-D-Glucosidase A presented similar affinities toward the four substrates (K-m in the range 0.43-0.5 mM) but displayed very different activities. Cellobiose and geranyl-beta-D-glucoside were degraded with respective catalytic constants of 200 mu mol min(-1) mg(-1) and 28 mu mol min(-1) mg(-1), whereas the degradation of malvidin-3-glucoside was very slow (k(cat) similar to 1 mu mol min(-1) mg(-1)). On the contrary, beta-D-glucosidase B displayed its maximum activity toward malvidin-3-glucoside (K-m similar to 0.11 mM, k(cat) similar to 50 mu mol min(-1) mg(-1)) and had no significant activity on geranyl-beta-D-glucoside and cellobiose (K-m similar to 0.25 mM, k(cat) similar to 0.4 mu mol min(-1) mg(-1)); thus, the two enzymes presented different potential applications to the fruit juice industry, aroma enhancing and liquefaction/maceration with beta-D-glucosidase A, and decolorization with beta-D-glucosidase B. (C) 1998 Elsevier Science Inc.