Bacterial Transferrin Receptor Complex: A complex of proteins that forms a receptor for TRANSFERRIN in BACTERIA. Many pathogenic bacteria utilize the transferrin-binding complex to acquire their supply of iron from serum.Transferrins: A group of iron-binding proteins that tightly bind two ferrate ions along with two carbonate ions. They are found in the bodily fluids of vertebrates where they act as transport and storage molecules for iron.Receptors, Transferrin: Membrane glycoproteins found in high concentrations on iron-utilizing cells. They specifically bind iron-bearing transferrin, are endocytosed with its ligand and then returned to the cell surface where transferrin without its iron is released.Transferrin: An iron-binding beta1-globulin that is synthesized in the LIVER and secreted into the blood. It plays a central role in the transport of IRON throughout the circulation. A variety of transferrin isoforms exist in humans, including some that are considered markers for specific disease states.