Effect of iron on sedimentation-velocity and gel filtration behaviour of transferrins from several vertebrates.

1. The effect of iron binding on the conformation of transferrins has been studied using analytical gel filtration and differential velocity sedimentation. 2. In all cases where bicarbonate is the anion the transferrin molecules undergo changes in Stokes' radius and sedimentation coefficient of the same order of magnitude, but of opposite sign. 3. Replacement of the bicarbonate ion with oxalate results in smaller changes in these two parameters. 4. In all cases except ovotranferrin, sheep serum transferrin, and human transferrin with oxalate as the anion, changes in Stokes' radius for the addition of the first and second iron atoms are similar. 5. For ovotransferrin and sheep transferrin it is necessary to postulate interaction between the iron-binding sites to account for the change in Stokes' radius caused by the second iron atom binding being greater than for the first. 6. Human transferrin with oxalate as the anion shows a greater change for the first atom bound than for the second which is consistent with the increased size of the oxalate ion compared with bicarbonate.