Abstract
The activity of nitrate reductase in cell-free extracts from tomato leaves is completely inhibited by 100 μM NaVO3 or VOCl2. In experiments in vivo vanadium ions inhibit the activity of the enzyme in 50 to 60 per cent. Addition of l mM vanadium to the medium on which tomato seedlings are grown causes after 24 h almost complete inhibition of nitrate reductase activity in cell-free extracts of the enzyme. Inhibition with vanadium may be abolished in experiments in vitro if the extract is treated with a rather concentrated EDTA solution or Sephadex G-25. The data obtained in this study indicate that vanadium ions in relatively low concentrations inhibit the activity of nitrate reductase in tomato seedlings both in vivo and in nitro.