Possible interaction between peroxidase and NAD(P)H-dependent nitrate reductase activities of plasma membranes of corn roots

Abstract

The relationship between the plasma membrane-bound NAD(P)H-nitrate reductase (NR) and a plasma membrane (PM)-bound peroxidase was investigated using highly purified PM vesicles isolated from corn roots. The PM-bound NR activity was strongly enhanced by MnCl 2 and SHAM, which stimulated peroxidase activity. Since both activities, the NAD(P)H-dependent NR and the peroxidase compete for NAD(P)H as electron donor, we propose a model in which a product of peroxidation is able to offer electrons to the nitrate reductase in a more reactive form with respect to NAD(P)H. Out hypothesis was confirmed by experiments in which the effects of inhibitors of peroxidative reactions, catalase, superoxide dismutase, and ascorbate on the PM-bound NR were studied. Results indicate that the putative electron donor for nitrate reduction could be a radicalic species, possibly NAD . . Furthermore, since cytochrome c decreased the activity of the plasma membrane-bound NAD(P)H-dependent NR, cytochrome b 557 might be the site of the enzyme accepting electrons from NAD . . Out results indicate that the PM environment of the NR may be involved in the extent of the membrane-associated nitrate reduction and that redox enzymes at the PM, the NAD(P)H-NR and a peroxidase-like NADH-oxidase, can interact.