Date of Award

Spring 1985

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

Abstract

This dissertation examines the use of computers in quantitative EPR spectroscopy. The computers used ranged from hand held calculators to large main frame systems. Applications discussed are protein assay calculations, an EPR minicomputer interface and software system and the modification of an existing EPR simulation program to include corrections for strains in the g and A tensors. The modification permits more accurate linewidth simulation for lines with large M(,I) values. The computer interface and software allows for the collection of EPR spectra, which can then be stored, scaled, added, subtracted (for comparison) and double integrated. The program enhances weak signals by signal averaging. Double integration was used to assist in the study of early iron binding in horse spleen apoferritin. Iron(II) was added to apoferritin followed by oxidation by a variety of methods. In all cases an iron(III) EPR signal was observed at g' = 4.3 which was attributed to mononuclear Fe(III) bound to the protein; this signal increased until 0.5 equivalent per subunit of added iron. In another experiment increasing amounts of Tb(III) were added to apoferritin solutions. Subsequent addition of 0.5 equivalent of iron(II) per subunit resulted in an Fe(III) signal that decreased as a function of added Tb(III). It was also found that ultracentrifugation of commercial ferritin yields a light, low iron content, fraction which showed a majority of the iron signal intensity relative to the heavy, iron rich, fraction. These results suggest that iron core starts to form at an initial binding site that lies between two adjacent subunits resulting in a 0.5 equivalent of binding site per subunit and that this site also serves as the nucleus of core formation within the ferritin molecule. As the core grows beyond 0.5 equivalents per subunit more of the mononuclear sites are converted into growing core. At 0.5 equivalents per subunit double integration shows that only 20% of the added iron is EPR active suggesting a majority of the added iron is present as polymeric iron (core) species.

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