Tunnel-Diodes and Catalytic Bias

Voltammetric methods in which the enzyme is adsorbed to an electrode are considered to measure catalytic bias. In these idireeti (unmediated by 

How eould this eatalytie bias be controlled One possibility is that the proton transfer pathway eould eontribute to specifieity (Peters et al., 1998). Another possibility is that differences in midpoint potential of the FeS clusters (or other redox sites) that constitute the intramolecular wire could be tuned to facilitate one of the two directions of the reaction. For example, these redox sites could best match the midpoint potentials of a particular oxidized or reduced electron carrier (Holm and Sander, 1999). Apparently, a conformational change in succinate dehydrogenase, coupled to the reduction of FAD, is responsible for its catalytic bias for fumarate reduction (Hirst et al., 1996). 

Acknowledgments. I wish to thank Juan Fontecilla-Camps, Anne Volbeda, Patricia Amara, Yvain Nicolet, and John Peters for supplying figures for this review. 

The structure and mechanism of iron-hydrogenases, Biochim. Biophys. Acta. 1020(2) 115nl45. 

Eccleston, E., and Howard, J. B., 1989, Iron-sulfur clusters of hydrogenase I and hydrogenase II of Clostridium pasteurianum, Proc. Natl. Acad. Sci. USA 8 6(13) 4932n4936. 

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