Dissociation of ferritins.

Apoferritins prepared from horse spleen and heart and rat heart and liver were dissociated by treatment with acetic acid (pH 1.3-3.0). Sedimentation velocity studies showed that apoferritins of spleen and liver (16-17 S) and heart (18-19 S) dissociated into material sedimenting near 3.2 S. Sedimentation equilibrium measurements determined that most of the material had a molecular weight of 38,000-43,000, corresponding to subunit dimers. Failure to dissociate into subunit monomers was confirmed by gel chromatography on Sephadex G-75 and G-150. With the exception of boiling in sodium dodecyl sulfate, further treatments with 0.1-0.4 M KCl, NaCl, 4-9 M urea, 0.01-0.5 M KSCN, 0.1-0.5% Triton X-100, 5-52% dimethylsulfoxide, 10% ethylene glycol, or 0.1% trifluoroacetic acid all failed to cause dissociation into individual subunits, as did exposure to 6 M guanidine-HCl or formic acid, or prior succinylation and/or nitration of the protein. Reassociation occurred between pH 4 and 7 but was not aided by the addition of Fe(II) or reducing agents. It is concluded that ferritins readily dissociate to subunit dimer units and that further dissociation does not occur without full denaturation of the protein.