Parahydrogen-enhanced magnetic resonance identification of intermediates in [Fe]-hydrogenase catalysis

Hydrogenases are widespread metalloenzymes used for the activation and production of molecular hydrogen. Understanding the catalytic mechanism of hydrogenases can help to establish industrial (bio)catalytic hydrogen production and conversion. Here we show the observation of so-far undetectable intermediates of [Fe]-hydrogenase in its catalytic cycle. We observed these intermediates by applying a signal-enhancing NMR technique based on parahydrogen. Molecular hydrogen occurs as orthohydrogen or parahydrogen, depending on its nuclear spin state. We found that catalytic conversion of parahydrogen by the [Fe]-hydrogenase leads to notably enhanced NMR signals (parahydrogen-induced polarization, PHIP). The observed signals encode information about how the [Fe]-hydrogenase binds hydrogen during catalysis. Our data support models of the catalytic mechanism that involve the formation of a hydride at the iron centre. Moreover, PHIP enabled studying the binding kinetics. This work demonstrates the hitherto unexploited power of PHIP to study catalytic mechanisms of hydrogenases.