Date of Award:

5-1989

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Chemistry and Biochemistry

Department name when degree awarded

Biochemistry/Molecular Biology

Committee Chair(s)

Steven D. Aust

Committee

Steven D. Aust

Committee

R. Coulombe

Committee

L. Piette

Committee

J. Morse

Committee

G.G. Smith

Abstract

The intent of this dissertation is to demonstrate that ferritin iron may be involved in alloxan, diquat, and radiation-dependent damage and that ceruloplasmin may afford protection by limiting the availability of ferritin iron. Initial studies demonstrated that the alloxan radical formed by glutathione-dependent reduction of alloxan reductively mobilized ferritin iron and the released iron catalyzed lipid peroxidation. SOD and catalase were without effect, whereas ceruloplasmin effectively inhibited both iron release and lipid peroxidation. Using 137Cs gamma-radiation it was demonstrated that radiolytically generated superoxide released iron from ferritin with an efficiency of 67%. Lipid peroxidation strictly required both superoxide and ferritin iron. Ceruloplasmin inhibited iron release and lipid peroxidation, presumably by the ability to reincorporate released iron back into ferritin. The phospholipid liposomes were shown to facilitate iron release from ferritin by serving as an iron chelator.

In another study, the factors influencing ceruloplasmin-dependent iron incorporation into (apo)ferritin was determined. Ceruloplasmin dependent iron incorporation into (apo)ferritin occurred only when the Fe(II) was bound to chelators which favor chelation of Fe(II) (i.e., AMP and histidine). Iron incorporation into liver apoferritin was greater than into heart apoferritin despite a similar extent of Fe(II) oxidation. Ferritin fractions containing between 1200 and 2400 atoms Fe/molecule ferritin incorporated the most iron and became fully saturated (4500 atoms Fe/molecule).

The mechanism of iron release from ferritin appears to be different depending upon the reductant. Superoxide-dependent iron release was affected by both the ferritin protein and the iron core, whereas diquat cation radical-dependent release was only affected by the ferritin protein. Ferritin prepared by loading iron into liver apoferritin with ceruloplasmin was similar to ferritin isolated from liver tissue with respect to the initial rate of superoxide-dependent iron release.

In another study, it was demonstrated that diquat administration to rats resulted in the release of iron from liver ferritin. Ferritin levels were unchanged and so it appears that iron release did not result from ferritin destruction and probably occurred as a result of reductive mobilization by either superoxide or the diquat cation radical.

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