Differential sedimentation-velocity and gel-filtration measurements on human apotransferrin and iron-transferrin.

Differential measurements of sedimentation velocity showed that binding of 2 atoms of iron per molecule of human apotransferrin caused an increase in s(0) (20,w) of about 1.8%. Gel-filtration experiments to compare the elution volumes of apotransferrin and transferrin radioactively labelled with iron showed that binding of the first atom to a molecule produced a decrease in Stokes radius of about 0.7%, and the binding of a second atom an equal decrement. These results confirmed that saturation of human transferrin with iron alters the conformation sufficiently to produce detectable changes in the hydrodynamic properties. They also indicate that the local changes brought about by successive addition of 2 atoms of iron are very similar, if not identical.