In order to obtain fungous myrosinase, Aspergillus sydowi IFO 4284 was cultured on a medium containing mustard seed extract for 2 weeks. Myrosinase in the broth was purified about 150 fold by precipitation with ammonium sulfate and chromatography on DEAE-cellulose and DEAE-Sephadex. Comparison of thioglucosidase and sulfatase activities of the myrosinase preparation using pH-activity, pH-stability and temperature-stability curves revealed no differences from each other. The chromatograms of the two activities on DEAE-Sephadex showed good agreement. Consequently, the myrosinase produced by Aspergillus sydowi was concluded to be a single β-thioglucosidase, not a mixture of thioglucosidase and sulfatase.The effects of various reagents on Aspergillus sydowi myrosinase were studied.The enzymatic activity was stimulated by cobalt (II), zinc (II) and magnesium ions and inhibited by mercury (II), iron (II) and copper (II) ions. However, metal-complexing agents, SH reagents and diisopropylfluorophosphate showed no...