Encyclopedia of Metalloproteins

Abstract

Synonyms 1,2-Dihydroxy-3-keto-5-thiomethylpent-1-ene dioxygenase; ARD; E2; E2'; EC 1.13.11.54 & 1.13.11.53 Definition Acireductone dioxygenase (ARD) catalyzes the penultimate reaction in the methionine salvage path-way (MSP), the oxidative addition of O 2 to 2-hydroxy-3-keto-thiomethylpent-1-ene. The ARD-catalyzed reaction represents a branch point in the MSP. The on-pathway reaction (Scheme 1) results in the forma-tion of formate and the keto-acid precursor of methio-nine, 4-thiomethyl-2-ketobutyrate. An off-pathway reaction (Scheme 2) results in the production of for-mate, carbon monoxide and 3-thiomethylpropionate. It has been shown that the identity of the metal bound in the ARD active site controls which of these two reac-tions occur. In the case of the enzyme isolated from Klebsiella oxytoca, KoARD, the first ARD to be char-acterized, the on-pathway enzyme (KoARD') binds Fe +2 and that catalyzing the off-pathway reaction (KoARD) binds Ni +2 . Co +2 and Mn +2 can replace V.N. Uversky et al. (eds.), Encyclopedia of Metalloproteins, DOI 10.1007/978-1-4614-1533-6, # Springer Science+Business Media New York 2013 Ni +2 in generating off-pathway activity, while Mg +2 confers partial on-pathway activity (Dai et al. 2001). The enzyme has since been identified in both prokary-otic and eukaryotic organisms, although catalytic activity and metal-binding preferences have only been thoroughly characterized for the K. oxytoca enzyme.