Studies on Myrosinase in Mustard Seed

Part V On the β-Glucosidase Activity of Myrosinase and the Interaction of Ascorbate with Myrosinase

Abstract

β-Glucosidase activity of mustard myrosinase was confirmed using p-nitrophenyl β-glucoside (p-NPG) as the substrate. p-NPG hydrolysis was not accelerated by 10^-3M ascorbate but was inhibited competitively by its higher concentrations. This result forms a distinct contrast with the activating effect of ascorbate in enzymatic sinigrin hydrolysis. The previously noticed feature of the ascorbate effect on the enzyme that the Km value for sinigrin hydrolysis increased after activation is explainable by the fact that ascorbate was a competitive inhibitor as well as a specific activator. A schematic model interpreting the interaction of ascorbate with the enzyme is proposed.