Purification and characterization of vanilla bean (Vanilla planifolia Andrews [bêta]-D glucosidase

Vanilla bean [bêta]-D-glucosidase was purified to apparent homogeneity by successive anion exchange, hydrophobic interaction, and siz-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°C at pH 7.0. Km values for [rô]-nitrophenyl-[bêta]-D-glueopyranoside and glucovanillin were 1.1 and 20.0 mM, respectively; Vmax values were 4.5 and 5.0 [mu]kat-mg-1. The [bêta]-D-glucosidase was competitively inhibited by glucono-[delta]-lactone and 1-deoxynojirimycin, with respective K. values of 670 and 152 [mu]M, and not inhibited by 2 M glucose. The [bêta]-D-glucosidase was not inhibited by [nu]-ethylmaleimide and DTNB and fully inhibited by 1.5-2 M2-mercaptoethanol and 1,4-dithiothreitol. The enzyme showed decreasing activity on [rô]-nitrophenyt-[bêta]-D-fucopyranoside, [rô]-nitrophenyl-[bêta]-Dglucopyranoside, [rô]-nitrophenyl-[bêta]-D-galactopyranoside, and [rô]-nitrophenyl-[bêta]-D-xylopyranoside. The enzyme was also active on prunasin, esculin, and salicin and inactive on cellobiose, gentiobiose, amygdalin, phloridzin, indoxyl-[bêta]-D-glucopyranoside, and quercetin-3-[bêta]-D-glucopyranoside. (Résumé d'auteur