Nitrite reductase

Nitrite reductase refers to any of several classes of enzymes that catalyze the reduction of nitrite. produces nitric oxide, using FAD as a cofactor. produces ammonia, with heme and calcium as cofactors.

Assimilatory nitrate reductase
Assimilatory nitrate reductase is an enzyme of the assimilative metabolism involved in reduction of nitrate to nitrite. The nitrite is immediately reduced to ammonia (probably via hydroxylamine) by the activity of nitrite reductase.

The term assimilatory refers to the fact that the product of the enzymatic activity remains in the organism. In this case, the product is ammonia which has an inhibitive effect on assimilatory nitrate reductase, thus ensuring that the organism produces the ammonia according to its requirements.