| Résumé | The influence of polar solvents on the hydrolysis of cellobiose (4-O-(β-Image -glucopyranosyl)-β-Image -glucopyranose) and p-NPG (p-nitrophenyl β-Image -glucopyranoside) by crude almond β-glucosidase has been measured. THF and acetonitrile diminish the initial reaction rate by a factor of 2 at a concentration of 10%, while DMF, DMSO and 2-methyl-2-butanol have little effect at this concentration, but induce a decrease at higher concentrations. The specificity constant Vmax/KM of the crude enzyme in aqueous solution was 200-fold higher for p-NPG than for cellobiose, indicating that between the two β-glucosidase activities present in almond, prunasin hydrolase may be more important than amygdalin hydrolase. However, the specificity constant for p-NPG was more affected by the presence of DMF, since it dropped six-fold for a 20% concentration of solvent while in the case of cellobiose, the drop was only 1.6-fold for the same solvent concentration. |
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