“…(11,12) Nitrate reductase (NR) is the first enzyme involved in nitrate assimilation in higher plants. (13) The enzyme catalyzes the rate-limiting and regulated step, the two-electron reduction of NO 3 -to NO 2 -, in the pathway of inorganic nitrogen assimilation. (14) The enzyme has been isolated from a variety of sources including algae, fungi, yeast, and higher plants (15,16) and, in all cases, has been shown to consist of multimeric proteins composed of identical subunits, each of which contains three cofactors, flavin adenine dinucleotide (FAD), a b-type cytochrome (cytochrome b557), and molybdenum cofactor prosthetic groups in a 1:1:1 stoichiometry per subunit.…”