Defense Date
1988
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Chemistry
First Advisor
Fred M. Hawkridge
Abstract
Quasi-reversible electron transfer kinetics are reported for sperm whale myoglobin reacting at tin-doped indium oxide electrodes. This reaction was studied by three different electrochemical or spectroelectrochemical methods; cyclic voltammetry (CV), single potential step chronoabsorptometry (SPS/CA) and derivative cyclic voltabsorptometry (DCVA). Kinetic parameters were determined from experiments which followed the purification of the protein,
the pretreatment of the electrode surface, and the removal of dioxygen from the sample solution. A formal heterogeneous electron transfer rate constant, k0′, of 2.6 (±0.5) x 10-5 cm/s and a transfer coefficient, α, of 0.48 (±0.05) were obtained using SPS/CA. These results are shown to correlate well with those obtained using a second spectroelectrochemical
method, DCVA. Both anodic and cathodic responses for the heterogeneous electron transfer of myoglobin can be observed using cyclic voltammetry, but the results are not as reproducible as optical methods.
Purification procedures for commercial samples are discussed. Kinetic parameters obtained after chromatography and after filtration are compared. SDS gel electrophoresis has been used to identify the deterrents to electron transfer. The non-uniformity of commercial samples of protein is noted.
Dioxygen effects are observed using the spectroelectrochemical technique, DCVA. They are due to the stability of the oxymyoglobin which forms immediately upon reduction of
myoglobin, and the lower difference molar absorptivity between oxymyoglobin and ferrimyoglobin as compared to that between ferromyoglobin and ferrimyoglobin. More quantitative information is obtained using an oxygen probe and cyclic voltammetry or double potential step chronocoulometry. By these methods, large effects of dioxygen are seen which are not removed by background subtraction. It is concluded that the amount of additional dioxygen present is, in some way, dependent on the myoglobin concentration, and that it must lodge within the heme pocket, although it is not always bound to the heme. Although oxymyoglobin is stable to oxidation at positive potentials, as the potential becomes more negative at potentials near the cathodic peak potential for myoglobin, reduction of dioxygen delivered to the electrode begins to occur. These results can be compared to the reduction of dioxygen by cytochrome oxidase in the mitochondria, and support the facilitated diffusion of dioxygen by myoglobin.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
4-29-2026