Nitrate reductase is a key enzyme involved in the first step of nitrate assimilation in plants, fungi and bacteria. H2O + NAD(+) + nitrite = H(+) + NADH + nitrate Binds 1 FAD per subunit. Binds 1 heme group per subunit. Binds 1 Mo-molybdopterin (Mo-MPT) cofactor per subunit. Regulated by the nitrogen source and controlled by the circadian rhythm. Homodimer. Maximum expression 2 hours after sunrise. Low expression found 2 hours before and 8 hours after sunrise. Belongs to the nitrate reductase family.