During receptor-mediated endocytosis of iron, Fe³⁺ is transported into cells via:
Vertebrates transport ferric iron safely via transferrin family to avoid oxidative Fenton radical damage and precipitation. Hepatocytes secrete apo-transferrin 80 kDa bilobed glycoprotein serum loads two Fe3+ each coordinated synergistically bidentate carbonate anion plus four protein ligands two tyrosines histidine aspartate each lobe producing salmon pink complex termed ferrotransferrin diferric transferrin. Doubly loaded species binds transferrin receptor TfR1 homodimer dissociation constant 1-10 nM neutral pH versus 50-fold lower affinity monoferric negligible apo providing selection iron
Ref: Lodish et al., MCB Figure 14-29: Ferrotransferrin carries Fe3+ for uptake via transferrin receptor.
