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(also siderophilin), any of a group of related complex proteins (glycoproteins) that transport Fe3+ iron ions in organisms. The carbohydrate component of transferrins constitutes approximately 5.5 percent. The molecular weight is approximately 80,000.
Transferrins occur in blood plasma, milk, and egg albumin (conalbumin). In blood plasma, their main functions are the transport of iron (with one molecule of transferrin binding two atoms of trivalent iron) to the reticulocytes, where hemoglobin is synthesized, and the maintenance of the Fe2+/Fe3+ ratio at a certain level. Upon electrophoresis of plasma proteins, transferrin is found in the β-globulin fraction. Transferrins are found in various genetically dependent forms, which have similar physical and chemical properties. A deficiency of transferrin in organisms leads to a number of pathological states caused by disruption of iron metabolism.