Xanthine oxidase in lentil (Lens esculenta) seedlings

Until recently there were no reports regarding the presence of xanthine oxidase (xanthine:oxygen oxidoreductase, EC 1.2.3.2) in plants. Direct evidence for its presence in lentil seedlings is reported here. Xanthine oxidase activity increases with the period of germination, reaching a maximum at 24 h and decreasing thereafter. The pH optimum for its activity is at pH 8.0. Almost equal activity is observed against xanthine and hypoxanthine. The Km for xanthine is 1.05 mM, and considerable inhibition is observed at high substrate concentration.