INVIVO EFFECT OF ORTHOVANADATE ON THE NITRATE REDUCTASE-ACTIVITY IN CUCUMBER ROOTS

Sodium orthovanadate (Na3VO4) at 500-mu-M concentration, strongly inhibited a NADH-dependent nitrate reduction (NADH:NR activity, E.C. 1.6.6.1) and Mo-pterin component activity (MVH:NR activity) in the nitrate reductase complex extracted from cucumber roots. However, orthovanadate had no effect on dehydrogenase activity measured by the reduction of ferricyanide (NADH:FR activity). It was suggested that the Mo-pterin component in the nitrate reductase molecule could be a site of orthovanadate inactivation in enzyme complex.