Heterogeneities in ferritin dimers as characterized by gel filtration, nuclear magnetic resonance, electrophoresis, transmission electron microscopy, and gene engineering techniques.

To understand the mechanism underlying the preferential dimerization of ferritin shells, we studied monomers and dimers from both horse spleen and recombinant horse L-apoferritin by using gel filtration, nuclear magnetic resonance, electrophoresis, transmission electron microscopy, and gene engineering techniques. Our study of the kinetics of dimer-monomer dissociation that is produced by heating revealed the presence of at least two types of dimers, namely, weakly and strongly linked dimers with activation energies of 124 +/- 14 and 157 +/- 16 kJ/mol, respectively. Our study using thiol reagents indicated that the dimerization in horse spleen ferritin is partially mediated by disulfide bridges being formed between H-chains. Our analysis of the components that resulted from the dimer-monomer dissociation further clarified that these dimers form interdigitation structures. In summary, five types of dimers were identified in horse spleen apoferritin: reversible dimers with very weak interaction, non-sulfide dimers with weak interaction, non-sulfide dimers with strong interaction, disulfide dimers linked only by disulfide bridges, and disulfide dimers linked by disulfide bridges and having other interactions.