Glycosidases of turnip leaf tissues

I. physiochemical properties of myrosinase and disaccharase enzymes
  • Sanaa T. El-Sayed
  • Etidal W. Jwanny


Four myrosinase (β-thioglucosidase EC. and seven disaccharase (β-fructofuranosidase, EC. isoenzymes were isolated from turnip leaves. The most active enzymes were isolated in pure form. Myrosinase and disaccharase mol wt was 62.0 × 103 and 69.5 × 103 dalton, respectively, on the basis of gel filtration on Sephadex G-200.

Myrosinase pH profile showed high activity between pH 5 and 7 with the optimum at pH 5.5. The purified enzyme was heat-stable for 60 min at 30°C with only loss of 24% of activity. Its activity is strongly inhibited (100%) by Pb2+, Ba2+, Cu2+ and Ca2+ ions, and activated (70%) by EDTA at 0.04M. The pure enzyme failed to hydrolyze amylose, glycogen, lactose, maltose, and sucrose. TheK m andV max values of myrosinase using sinigrin as specific substrate was 0.045 mM and 2.5 U, respectively.

The maximal activity of disaccharase enzyme was obtained at pH 4–5 and 35–37°C. The enzyme was heat-stable at 30°C for 30 min with only 10% loss of its activity. Its activity is strongly activated (70–240%) by Ca2+, Ba2+, Cu2+, and EDTA at 0.01M. The enzyme activity is specific to the disaccharide sucrose and failed to hydrolyze other disaccharides (maltose and lactose). TheK m andV max of disaccharase were 0.123 mM and 3.33 U, respectively.

Index Entries

Turnip leaves myrosinase (β-thioglucosidase) disaccharase (β-fructofuranosidase) Sephadex G-200 


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Copyright information

© Humana Press Inc. 1994

Authors and Affiliations

  • Sanaa T. El-Sayed
    • 1
  • Etidal W. Jwanny
    • 1
  1. 1.Biochemistry DepartmentNational Research CenterCairoEgypt

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