Purification and characterization of an intracellular beta-glucosidase from the methylotrophic yeast Pichia pastoris
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Pichia pastoris beta-glucosidase was purified to apparent homogeneity by salting out with ammonium sulfate, gel filtration, and ion-exchange chromatography with Q-Sepharose and CM-Sepharose. The enzyme is a tetramer (275 kD) made up of four identical subunits (70 W). The pH optimum is 7.3, and it is fairly stable in the pH range 5.5-9.5. The temperature optimum is 40 degrees C. The purified P-glucosidase is effectively active on p-/o-nitrophenyl-beta-D-glucopyranosi des (p/o-NPG) and 4-methylumbelliferyl-beta-D-glucopyranoside (4-MUG) with K-m, values of 0.12, 0.22, and 0.096 mM and V-max. values of 10.0, 11.7, and 6.2 mu mol/min per mg protein, respectively It also exhibits different levels of activity against p-nitrophenyl-l-thio-beta-D-glueopyranoside, cellobiose, gentiobiose, amygdalin, prunasin, salicin, and linamarin. The enzyme is competitively inhibited by gluconolactone, p-/o-nitrophenyl-beta-D-fucopyranosides (p-/o-NPF), and glucose against p-NPG as substrate. o-NPF is the most effective inhibitor of the enzyme activity with K, value of 0.41 mM. The enzyme is more tolerant to glucose inhibition with K-i-value of 7.2 mM for p-NPG. Pichia pastoris has been employed as a host for the functional expression of heterologous beta-glucosidases and the risk of high background P-glucosidase activity is discussed.