Purification and characterization of vanilla bean (Vanilla planifolia Andrews) β-D-glucosidase

Vanilla bean P-D-glucosidase was purified to apparent homogeneity by successive anion exchange, hydrophobic interaction, and size-exclusion chromatography. The enzyme is a tetramer (201 kDa) made up of four identical subunits (50 kDa). The optimum pH was 6.5, and the optimum temperature was 40 degreesC at pH 7.0. Km values for p-nitrophenyl-beta-D-glucopyranoside and glucovanillin were 1.1 and 20.0 mM, respectively; V-max values were 4.5 and 5.0 mukat.mg(-1). The P-D-glucosidase was competitively inhibited by glucono-delta-lactone and 1-deoxynojirimycin, with respective K-i values of 670 and 152 muM, and not inhibited by 2 M glucose. The P-D-glucosidase was not inhibited by N-ethylmaleimide and DTNB and fully inhibited by 1.5-2 M 2-mercaptoethanol and 1,4-dithiothreitol. The enzyme showed decreasing activity on p-nitrophenyl-beta-D-fucopyranoside, p-nitrophenyl-beta-D-glucopyranoside, p-nitrophenyl-beta-D-galactopyranoside, and p-nitrophenyl-beta-D-xylopyranoside. The enzyme was also active on prunasin, esculin, and salicin and inactive on cellobiose, gentiobiose, amygdalin, phloridzin, indoxyl-beta-D-glucopyranoside, and quercetin-3-beta-D-glucopyranoside.