Acireductone dioxygenase (Ni2+-requiring) () is an enzyme that catalyzes the chemical reaction
The two substrates of this enzyme are 1,2-dihydroxy-5-(methylthio)pent-1-en-3-one and oxygen. Its products are 3-(methylthio)propionic acid, formic acid, and carbon monoxide.
This enzyme belongs to the family of oxidoreductases, specifically those acting on single donors with O<sub>2</sub> as oxidant and incorporation of two atoms of oxygen into the substrate (oxygenases). The oxygen incorporated need not be derived from O<sub>2</sub>. The systematic name of this enzyme class is 1,2-dihydroxy-5-(methylthio)pent-1-en-3-one:oxygen oxidoreductase (formate- and CO-forming). Other names in common use include ARD, 2-hydroxy-3-keto-5-thiomethylpent-1-ene dioxygenase (ambiguous), acireductone dioxygenase (ambiguous), and E-2. It participates in the methionine salvage pathway in the bacterium Klebsiella pneumoniae.
The protein component of the enzyme is identical to that in acireductone dioxygenase (iron(II)-requiring), which uses iron(II) rather than nickel(II) as the metal at the centre of the active site.