In enzymology, a toluene dioxygenase is an enzyme that catalyzes the chemical reaction The 4 substrates of this enzyme are toluene, NADH, H+, and O2, whereas its two products are (1S,2R)-3-methylcyclohexa-3,5-diene-1,2-diol and NAD+. This enzyme belongs to the family of oxidoreductases, specifically those acting on paired donors, with O2 as oxidant and incorporation or reduction of oxygen. The oxygen incorporated need not be derived from O2 with NADH or NADPH as one donor, and incorporation of two atoms o oxygen into the other donor. The systematic name of this enzyme class is toluene,NADH:oxygen oxidoreductase (1,2-hydroxylating). This enzyme is also called toluene 2,3-dioxygenase. This enzyme participates in toluene and xylene degradation.