Transferrin, a highly prevalent serum glycoprotein that functions to transport iron to tissues, is present in serum at 3–4 mg/mL and binds iron firmly yet reversibly. Transferrin comprises 679 amino acid residues, is around 80 kDa in size, and possesses two high-affinity Fe3+ -binding sites, one in the N-terminal domain and the other in the C-terminal domain. The half-life of human transferrin is reported to be either 10–12 days or 7–10 days.
For more: https://half-life-extension.creative-biolabs.com/transferrin-fusion-based-half-life-extension-service.htm