Inhibition of nitrate reductase from tomato leaves by adenosine-5'-diphosphate

ADP was found to inhibit the activity of nitrate reductase fromtomato leaves in vitro. No effects of ATP, AMP, adenosine andadenine could be detected. Orthophosphate promoted activityonly in the presence of high concentrations of NADH₂. It is suggested that nitrate reductase possesses characteristicsof a regulatory enzyme and that ADP brings about a transformationin the conformation of the enzyme, with a resulting decreasein its activity. (Received February 29, 1968; )