Site-selective protonation of the one-electron reduced cofactor in [FeFe]-hydrogenase

Laun, K. and Baranova, I. and Duan, J. and Kertess, L. and Wittkamp, F. and Apfel, U.-P. and Happe, T. and Senger, M. and Stripp, S.T.

Volume: 50 Pages: 3641-3650
DOI: 10.1039/d1dt00110h
Published: 2021

Hydrogenases are bidirectional redox enzymes that catalyze hydrogen turnover in archaea, bacteria, and algae. While all types of hydrogenase show H2oxidation activity, [FeFe]-hydrogenases are excellent H2evolution catalysts as well. Their active site cofactor comprises a [4Fe-4S] cluster covalently linked to a diiron site equipped with carbon monoxide and cyanide ligands. The active site niche is connected with the solvent by two distinct proton transfer pathways. To analyze the catalytic mechanism of [FeFe]-hydrogenase, we employoperandoinfrared spectroscopy and infrared spectro-electrochemistry. Titrating the pH under H2oxidation or H2evolution conditions reveals the influence of site-selective protonation on the equilibrium of reduced cofactor states. Governed by pKadifferences across the active site niche and proton transfer pathways, we find that individual electrons are stabilized either at the [4Fe-4S] cluster (alkaline pH values) or at the diiron site (acidic pH values). This observation is discussed in the context of the complex interdependence of hydrogen turnover and bulk pH. © The Royal Society of Chemistry 2021.

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