CO synthesized from the central one-carbon pool as source for the iron carbonyl in O 2 -tolerant [NiFe]-hydrogenase

Significance Activation of dihydrogen is by far not a trivial catalytic reaction. Microbes have evolved sophisticated hydrogenases with complex transition metal centers to get access to H 2 . A recurring feature of these centers is the presence of iron atoms equipped with carbon monoxide ligands. In case of [NiFe]-hydrogenases, which contain a NiFe(CN) 2 CO catalytic center, biosynthesis of the toxic CO ligand remained elusive. We show that [NiFe]-hydrogenases that are catalytically active in the presence of dioxygen use a dedicated maturase for CO ligand synthesis under aerobic conditions. CO is derived from the most oxidized intermediate of the central one-carbon metabolism, formyl-tetrahydrofolate. This discovery contributes a so far unknown reaction to the one-carbon metabolism and opens perspectives for chemical and of bioinspired catalysis.