• Lubitz, Wolfgang
• Adamska-Venkatesh, Agnieszka
• Siebel, Judith F.
• Yoda, Yoshitaka
• Rauchfuss, Thomas B.
• Tamasaku, Kenji
• Gilbert-Wilson, Ryan
• Reijerse, Edward J.
• Pelmenschikov, Vladimir
• Gee, Leland B.
• Cramer, Stephen P.
• Pham, Cindy C.

Abstract

[FeFe]-hydrogenases catalyze the reversible reduction of protons to molecular hydrogen with extremely high efficiency. The active site ("H-cluster") consists of a [4Fe-4S]H cluster linked through a bridging cysteine to a [2Fe]H subsite coordinated by CN- and CO ligands featuring a dithiol-amine moiety that serves as proton shuttle between the protein proton channel and the catalytic distal iron site (Fed). Although there is broad consensus that an iron-bound terminal hydride species must occur in the catalytic mechanism, such a species has never been directly observed experimentally. Here, we present FTIR and nuclear resonance vibrational spectroscopy (NRVS) experiments in conjunction with density functional theory (DFT) calculations on an [FeFe]-hydrogenase variant lacking the amine proton shuttle which is stabilizing a putative hydride state. The NRVS spectra unequivocally show the bending modes of the terminal Fe-H species fully consistent with widely accepted models of the catalytic cycle.

Topics

• density
• impedance spectroscopy
• cluster
• theory
• experiment
• Hydrogen
• density functional theory
• iron
• amine
• vibrational spectroscopy