FeFe hydrogenase reductive inactivation and implication for catalysis

We show that FeFe hydrogenases inactivate at tow potential, in a complex process that is mostly reversible. A form of the enzyme that is produced slowly and reversibly under reductive conditions has no proton activity under reductive conditions, although it can still oxidize H-2 under oxidative conditions. This suggests that the so-called super-reduced state of the active site H-cluster is not part of the normal catalytic cycle. We also discuss our findings in relation to the optimization of H-2-photoproduction devices based on FeFe hydrogenases that receive electrons from low potential photosensitizers.