Withania somnifera (Ashwagandha): a novel source of L-asparaginase.

Different parts of plant species belonging to Solanaceae and Fabaceae families were screened for L-asparaginase enzyme (E.C.3.5.1.1.). Among 34 plant species screened for L-asparaginase enzyme, Withania somnifera L. was identified as a potential source of the enzyme on the basis of high specific activity of the enzyme. The enzyme was purified and characterized from W. somnifera, a popular medicinal plant in South East Asia and Southern Europe. Purification was carried out by a combination of protein precipitation with ammonium sulfate as well as Sephadex-gel filtration. The purified enzyme is a homodimer, with a molecular mass of 72 +/- 0.5 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and size exclusion chromatography. The enzyme has a pH optimum of 8.5 and an optimum temperature of 37 degrees C. The Km value for the enzyme is 6.1 x 10(-2) mmol/L. This is the first report for L-asparaginase from W. somnifera, a traditionally used Indian medicinal plant.