Non‐Coordinative Binding of O 2 at the Active Center of a Copper‐Dependent Enzyme

Molecular oxygen (O 2 ) is a sustainable oxidation reagent. O 2 is strongly oxidizing but kinetically stable and its final reaction product is water. For these reasons learning how to activate O 2 and how to steer its reactivity along desired reaction pathways is a longstanding challenge in chemical research. [1] Activation of ground‐state diradical O 2 can occur either via conversion to singlet oxygen or by one‐electron reduction to superoxide. Many enzymes facilitate activation of O 2 by direct fomation of a metal‐oxygen coordination complex concomitant with inner sphere electron transfer. The formylglycine generating enzyme (FGE) is an unusual mononuclear copper enzyme that appears to follow a different strategy. Atomic‐resolution crystal structures of the precatalytic complex of FGE demonstrate that this enzyme binds O 2 juxtaposed, but not coordinated to the catalytic Cu I . Isostructural complexes that contain Ag I instead of Cu I or nitric oxide instead of O 2 confirm that formation of the initial oxygenated complex of FGE does not depend on redox activity. A stepwise mechanism that decouples binding and activation of O 2 is unprecedented for metal‐dependent oxidases, but is reminiscent of flavin‐dependent enzymes.