Increase in in vivo Nitrate Reductase Activity in Bean Leaf Segments in the Presence of Ethanol

Summary The substrate inducibility of in vivo nitrate reductase (NR, EC 1.6.6.1) activity in bean leaf segments increased with the supply of 10 to 100 mM ethanol. Ethanol also increased soluble protein, but to a lesser extent while it inhibited the peroxidase activity. The increase in enzyme activity in the presence of ethanol was more pronounced at lower concentrations of nitrate than at higher. While supply of cycloheximide inhibited the substrate induction of nitrate reductase, it had little effect on increase in enzyme activity due to ethanol. Chloramphenicol inhibited the ethanol-induced increase slightly, while tungstate completely blocked it. While glucose had little effect, sucrose increased enzyme activity substantially in the presence of nitrate. Supply of ethanol had no effect on enzyme activity in the presence of sucrose, although it increased enzyme activity in the presence of glucose. Malonate, in a concentration of 2 to 10 mM inhibited enzyme activity both in the absence as well as in the presence of ethanol. The experiments demonstrate that ethanol increased nitrate reductase activity, by increasing nitrate uptake and transport, and possibly also by accelerating the conversion of inactive apoenzyme to active enzyme molecules.