Nitrate reductase is a key enzyme involved in the first step of nitrate assimilation in plants, fungi and bacteria. H2O + NADP(+) + nitrite = H(+) + NADPH + nitrate Binds 1 FAD per subunit. Binds 1 heme group per subunit. The heme group is called cytochrome b-557. Binds 1 Mo-molybdopterin (Mo-MPT) cofactor per subunit. Nitrogen metabolism; nitrate reduction (assimilation). Homodimer. Its expression is highly regulated and responds rapidly to nitrate induction and to nitrogen repression. Belongs to the nitrate reductase family.