Reduction Potentials of [FeFe]-Hydrogenase Accessory Iron–Sulfur Clusters Provide Insights into the Energetics of Proton Reduction Catalysis

• Published in: Journal of the American Chemical Society 2017-07, Vol.139 (28), p.9544-9550
• Main Authors: Artz, Jacob H, Mulder, David W, Ratzloff, Michael W, Lubner, Carolyn E, Zadvornyy, Oleg A, LeVan, Axl X, Williams, S. Garrett, Adams, Michael W. W, Jones, Anne K, King, Paul W, Peters, John W
• Format: Article
• Language: English
• Subjects: 09 BIOMASS FUELS; [FeFe]-hydrogenase; catalysis; Clostridium pasteurianum; electron paramagnetic resonance; electron-transfer; iron sulfur clusters; potentiometric titrations; spectral deconvolution
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.7b02099

An [FeFe]-hydrogenase from Clostridium pasteurianum, CpI, is a model system for biological H2 activation. In addition to the catalytic H-cluster, CpI contains four accessory iron–sulfur [FeS] clusters in a branched series that transfer electrons to and from the active site. In this work, potentiometric titrations have been employed in combination with electron paramagnetic resonance (EPR) spectroscopy at defined electrochemical potentials to gain insights into the role of the accessory clusters in catalysis. EPR spectra collected over a range of potentials were deconvoluted into individual components attributable to the accessory [FeS] clusters and the active site H-cluster, and reduction potentials for each cluster were determined. The data suggest a large degree of magnetic coupling between the clusters. The distal [4Fe-4S] cluster is shown to have a lower reduction potential (∼