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The Redox Couple Of The Cytochrome C Cyanide Complex: The Contribution Of Heme Iron Ligation To The Structural Stability, Chemical Reactivity, And Physiological Behavior Of Horse Cytochrome C, Abel Schejter, Michael D. Ryan, Erica R. Blizzard, Chongyao Zhang, Emanuel Margoliash, Benjamin A. Feinberg

Chemistry Faculty Research and Publications

Contrary to most heme proteins, ferrous cytochrome c does not bind ligands such as cyanide and CO. In order to quantify this observation, the redox potential of the ferric/ferrous cytochrome c–cyanide redox couple was determined for the first time by cyclic voltammetry. Its E⁰′ was −240 mV versus SHE, equivalent to −23.2 kJ/mol. The entropy of reaction for the reduction of the cyanide complex was also determined. From a thermodynamic cycle that included this new value for the cyt c cyanide complex E⁰′, the binding constant of cyanide to the reduced protein was estimated to …