Component of the 2,4-dinitrotoluene dioxygenase (DNTDO) multicomponent enzyme system which catalyzes the incorporation of both atoms of molecular oxygen into 2,4-dinitrotoluene (DNT) to form 4-methyl-5-nitrocatechol (MNC) and nitrite. The beta subunit seems to have a structural role in the holoenzyme. Also able to convert naphthalene to cis-(1R,2S)-dihydroxy-1,2-dihydronaphthalene. The 2,4-dinitrotoluene dioxygenase (DNTDO) multicomponent enzyme system is composed of an electron transfer component and a dioxygenase component (iron sulfur protein (ISP)). The electron transfer component is composed of a ferredoxin reductase (DntAa) and a ferredoxin (DntAb), and the dioxygenase component is formed of a large alpha subunit (DntAc) and a small beta subunit (DntAd). Belongs to the bacterial ring-hydroxylating dioxygenase beta subunit family.