Document Type

Dissertation - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)


Cytochrome c ( cyt c) is a heme containing protein of the mitochondrial electron transport chain. Cyt c transfers electrons from cytochrome reductase to cytochrome oxidase. The reactivity of cyt c with the inorganic reagents, cobalt phenanthroline, (Co(phen)33 +), and cobalt oxalate, (Co(oxh3-) was studied. The effects of ionic strength, pH, amino acid side chain modifications to cyt c, and association of cyt c with synthetic vesicles on the reactivity of cyt c have been determined. Generally, oxidation of cyt c associated with membranes by Co(phen)3(Cl04)3 is faster than solution cyt c. The trend is reversed for the oxidation of cyt c by K3Co(ox)3; the rate is slower when associated with membranes. The activation enthalpy is larger for the oxidation of cyt c by Co(phen)3 3 + than Co(ox)l-. The activation entropy is more negative for the oxidation of cyt c by Co(ox)?- than Co(phen)3 3+ . Photooxidation, chloramine T oxidation, and sulfonyl chloride modification of cyt c reveal that Met-80, Met-65 and Lys-79 are important in regulation of the open and closed forms of the protein. Photomodification of cyt c yields a protein whose reactivity is similar to native cyt c, however the association of PM cyt c with vesicles yields a system that is much more reactive than vesicle-bound native cyt c. The chloramine T modification of cyt c to a sulfoxide at both Met-65 and 80 destroys the ability of the protein to open and close substantiating that Met-65 is located in the hinge region and is important for conformational changes in the protein. The EPR spectra of chloramine T modified cyt c show the loss of Met-80 giving an open heme crevice and a new high-spin form. The sulfonyl chloride modifications yielded proteins whose reactivity toward Co(ox)l- and Co(phen)3 3+ are essentially the same as native cyt c. The EPR spectra of the sulfonyl chloride derivatives display a strong free radical signal due to the oxidation of the modifying fluorophore.

Library of Congress Subject Headings

Cytochrome c -- Reactivity.
Oxidation-reduction reaction.
Cobalt compounds.



Number of Pages



South Dakota State University