4-nitrocatechol 4-monooxygenase () is an enzyme with systematic name 4-nitrocatechol,NAD(P)H:oxygen 4-oxidoreductase (4-hydroxylating, nitrite-forming).This enzyme catalyses the following chemical reaction:
The four substrates of this enzyme are 4-nitrocatechol, reduced nicotinamide adenine dinucleotide (NADH), oxygen, and a proton. Its products are hydroxy-1,4-benzoquinone, oxidised NAD<sup>+</sup>, water, and nitrous acid. It is a flavoprotein that uses flavin adenine dinucleotide as a cofactor.