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ARD/ARD' family The two acireductone dioxygenase enzymes (ARD and ARD', previously known as E-2 and E-2') from Klebsiella pneumoniae share the same amino acid sequence, but bind different metal ions: ARD binds Ni2+, ARD' binds Fe2+. ARD and ARD' can be experimentally interconverted by removal of the bound metal ion and reconstitution with the appropriate metal ion. The two enzymes share the same substrate, 1,2-dihydroxy-3-keto-5-(methylthio)pentene, but yield different products. ARD' yields the alpha-keto precursor of methionine (and formate), thus forming part of the ubiquitous methionine salvage pathway that converts 5'-methylthioadenosine (MTA) to methionine. This pathway is responsible for the tight control of the concentration of MTA, which is a powerful inhibitor of polyamine biosynthesis and transmethylation reactions. ARD yields methylthiopropanoate, carbon monoxide and formate, and thus prevents the conversion of MTA to methionine. The role of the ARD catalyzed reaction is unclear: methylthiopropanoate is cytotoxic, and carbon monoxide can activate guanylyl cyclase, leading to increased intracellular cGMP levels. This family also contains other members, whose functions are not well characterized. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",