Sources of reducing power for nitrate reduction in spinach leaves.

The possible source of NADH, the energy donor for nitrate reductase (EC 1.6.6.1), has been studied using an in vivo assay involving freezing the material (leaves of Spinacea oleracea L.) in liquid nitrogen in order to render the tissue permeable to added substrates. Glycolysis and the pentose phosphate pathway were capable of generating NADH through glyceraldehyde-3-phosphate dehydrogenase. Malate and isocitrate were also capable of generating NADH white other organic acids tested were not, including glycolate which was ineffective even under anaerobic conditions.