Ferric‐citrate reductase activity of nitrate reductase and it's role in iron assimilation by plants

Abstract

Abstract Squash cotyledon and corn leaf NADH:nitrate reductase (NR) catalyze the reduction of Fe (III)‐citrate, as shown by trapping the reduced iron with ferrozine. The co‐identity of NR as a catalyst for both nitrate and iron reduction was shown by the co‐purification and co‐electrophoresis of the two activities with both partially pure and homogeneous enzyme forms. In addition, the Fe (III)‐citrate reductase activity had a pH optimum and substrate kinetics consistent with an enzymic reaction, and was inhibited by rabbit antiserum which had been prepared against homogeneous NADH:NR. Our previous studies with various inhibitors showed that Fe (III)‐citrate was directly reduced by NR, but at a site separate from the nitrate reducing site. A role for the Fe (III)‐citrate reductase activity of NR in the remoblization of recently transported iron is described in relation to the role of this enzyme in nitrate assimilation.