Defense Date


Document Type


Degree Name

Doctor of Philosophy



First Advisor

Fred M. Hawkridge


Spectroelectrochemical and electrochemical methods have been used to investigate the characteristics of heterogeneous electron transfer between cytochrome c and indium oxide electrodes. Direct electron transfer between cytochrome c and solid electrodes is of interest due to the interfacial character of electron transfer between the protein and its membrane-bound physiological redox partners. The conformation of ferricytochrome c is affected more by changes in temperature or pH than is its reduced form, ferrocytochrome c. This difference in conformational stability is attributed to the +1 charge of the heme in ferricytochrome c that is largely embedded in the hydrophobic interior of the enzyme.

A linear temperature dependence of the formal potential of cytochrome c was observed from 5 to ≥ 55 °C in neutral and acidic media. This behavior is attributed to a linear variation in the conformation of ferricytochrome c that results in an increase in solvent exposure of the solvent- exposed heme edge. A break in the linear temperature dependence of the formal potential occurred at 40 °C in alkaline media. This reflects a distinct conformational change that accompanies the onset of thermal denaturation of ferricytochrome c. The change in reaction center entropy, Asrc°, of ca. -13 eu in neutral and acidic media (5 to ≥ 55 °C) and in alkaline media (below 40 °C) is appropriate for the small shift to a more stable conformation of cytochrome c that occurs upon reduction.

The heterogeneous electron transfer rate constant, k°', of cytochrome c exhibited a biphasic temperature dependence with a maximum value obtained at different temperatures, but at the same formal potential in binding and nonbinding neutral media. This indicates that there is an optimum conformation of ferricytochrome c for facile heterogeneous electron transfer. Adsorption of reactant and product was detected. The strength and type of adsorption were found to be temperature- and pH-dependent. The characteristics of electron transfer between cytochrome c and an electrode depend on bulk solvent properties and electrode surface characteristics.


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