Purification and characterization of myrosinase from horseradish (Armoracia rusticana) roots

Myrosinase (β-thioglucoside glucohydrolase; EC 3.2.3.147) from horseradish (Armoracia rusticana) roots was purified to homogeneity by ammonium sulfate fractionation, Q-sepharose, and concanavalin A sepharose affinity chromatography. The purified protein migrated as a single band with a mass of about 65 kDa on SDS-polyacrylamide gel electrophoresis. Using LC-MS/MS, this band was identified as myrosinase. Western blot analysis, using the anti-myrosinase monoclonal antibody 3D7, showed a single band of about 65 kDa for horseradish crude extract and for the purified myrosinase. The native molecular mass of the purified myrosinase was estimated, using gel filtration, to be about 130 kDa. Based on these data, it appeared that myrosinase from horseradish root consists of two subunits of similar molecular mass of about 65 kDa. The enzyme exhibited high activity at broad pH (pH 5.0-8.0) and temperature (37 and 45 °C). The purified enzyme remained stable at 4 °C for more than 1 year. Using sinigrin as a substrate, the Km and Vmax values for the purified enzyme were estimated to be 0.128 mM and 0.624 μmol min-1, respectively. The enzyme was strongly activated by 0.5 mM ascorbic acid and was able to breakdown intact glucosinolates in a crude extract of broccoli.