Electron-microscopic and chemical studies of oligomers in horse ferritin |
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Authors: | M A Williams and Pauline M Harrison |
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Institution: | Department of Human Biology and Anatomy, University of Sheffield, S10 2TN;Department of Biochemistry, University of Sheffield, S10 2TN |
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Abstract: | Horse ferritin was fractionated both by starch-gel electrophoresis and by gel filtration on Sephadex G-200. Monomer fractions contained up to 98% of monomer and oligomer fractions up to 76% of oligomers as determined by quantitative electron microscopy. Percentages obtained from electron micrographs correlated well with analytical starch-gel electrophoretograms and ultracentrifuge patterns. Amino acid analyses of monomer- and oligomer-enriched fractions showed no significant differences. Ferritin oligomers did not apparently dissociate on dilution for electron microscopy or on storage. Apoferritin dimers were stable in 0·01m-phosphate buffer at dilutions down to 0·19mg./ml. as shown by ultracentrifugation. Chemical studies indicated that the intermolecular bonds in oligomers are resistant to a variety of reagents and conditions, including those that would be expected to attack disulphide, peptide and ester linkages respectively. Partial disaggregation was achieved at high pH values and in 67% (v/v) acetic acid. Centre-to-centre intermolecular distances in dimers were found to be about 100å. Three main types of trimer configuration were found and a variety of tetramers and pentamers. These configurations are described and discussed. |
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