| Autor: |
Artz JH; Institute of Biological Chemistry, Washington State University , 258 Clark Hall, Pullman, Washington 99163, United States., Mulder DW; Biosciences Center, National Renewable Energy Laboratory , 15013 Denver West Parkway, Golden, Colorado 80401, United States., Ratzloff MW; Biosciences Center, National Renewable Energy Laboratory , 15013 Denver West Parkway, Golden, Colorado 80401, United States., Lubner CE; Biosciences Center, National Renewable Energy Laboratory , 15013 Denver West Parkway, Golden, Colorado 80401, United States., Zadvornyy OA; Institute of Biological Chemistry, Washington State University , 258 Clark Hall, Pullman, Washington 99163, United States., LeVan AX; Department of Chemistry and Biochemistry, Montana State University , 224 Chemistry and Biochemistry Building, Bozeman, Montana 59717, United States., Williams SG; School of Molecular Sciences, Arizona State University , P.O. Box 871604, Tempe, Arizona 85287, United States., Adams MWW; B216B Life Sciences Complex, Department of Biochemistry, The University of Georgia , Athens, Georgia 30602, United States., Jones AK; School of Molecular Sciences, Arizona State University , P.O. Box 871604, Tempe, Arizona 85287, United States., King PW; Biosciences Center, National Renewable Energy Laboratory , 15013 Denver West Parkway, Golden, Colorado 80401, United States., Peters JW; Institute of Biological Chemistry, Washington State University , 258 Clark Hall, Pullman, Washington 99163, United States. |
| Abstrakt: |
An [FeFe]-hydrogenase from Clostridium pasteurianum, CpI, is a model system for biological H 2 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 (∼ < -450 mV) than the other clusters, and molecular docking experiments indicate that the physiological electron donor, ferredoxin (Fd), most favorably interacts with this cluster. The low reduction potential of the distal [4Fe-4S] cluster thermodynamically restricts the Fd ox /Fd red ratio at which CpI can operate, consistent with the role of CpI in recycling Fd red that accumulates during fermentation. Subsequent electron transfer through the additional accessory [FeS] clusters to the H-cluster is thermodynamically favorable. |
