Transferrin binds zinc at a site different from the iron-binding site

MIchio Katagi; Rintaro Seki; Yasunaga Yoshikawa; Taisuke Kitano; Koichi Orino

doi:10.5455/JRVS.20240724010345

Abstract
Background: Bovine apotransferrin strongly binds beads immobilized with zinc ion, indicating that transferrin carry zinc ion as well as iron.
Aim: The aim of this study is to elucidate the binding mechanism between zinc ion and transferrin, because, if zinc ion binding site is same binding site with iron, zinc ion competes with iron in the same binding site.
Methods: This study prepared beads which was immobilized with apotransferrin or zinc ion for the binding analysis of bovine transferrin with zinc ion. After binding of bovine apotransferrin with zinc-ion immobilized beads, the binding of apotransferrin with iron was examined.
Results: Beads immobilized with bovine apo-transferrin showed significantly lower zinc recovery compared with control beads that showed almost complete recovery of zinc ions derived from zinc sulfate added to each bead solution. Bovine apo- and holo-transferrin bound to zinc ion–immobilized beads, and holo-transferrin still bound iron even when binding to the beads. Zinc ion-binding apo-transferritin incorporated iron in the presence of ferrous ammonium sulfate and horse spleen apoferritin with ferroxidase.
Conclusion: These results suggest that transferrin directly binds zinc ions at sites other than iron-binding sites.

Key words: apo-transferrin, ferroxidase, holo-transferrin, iron, zinc