DOI

https://doi.org/10.25772/5MYM-CB67

Defense Date

1986

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Fred M. Hawkridge

Abstract

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.

Comments

Scanned, with permission from the author, from the original print version, which resides in University Archives.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

11-28-2017

Included in

Chemistry Commons

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