Heterogeneity of horse spleen ferritin and apoferritin: Comparison of electrophoretic and chromatographic fractions

Horse spleen ferritin and apoferritin each separate into several analogous components in gel electrophoresis. Sedimentation studies indicate that the major components are related as monomer, dimer, and trimer, and that the electrophoretic separation is due to differences in molecular size or shape rather than to differences in charge. Disulfide bonds do not appear to be involved in the formation of the aggregates. Moreover, the pattern of aggregation could not be altered by various agents which might be expected to disrupt macromolecular aggregates. Chromatography of ferritin on DEAE-cellulose reveals a different and unstable order of heterogeneity, not related to aggregate size. No significant difference in amino acid composition or in “fingerprints” of tryptic peptides of the DEAE fractions could be shown. Fractionation may be due to conformational differences among ferritin molecules.