Which of the following proteins is most responsible for iron transport in the plasma?
ExplanationIron absorbed from the diet or released from stores circulates in the plasma bound to transferrin, the iron transport protein. Transferrin that carries iron exists in two forms—mono-ferric (one iron atom) or ferric (two iron atoms). Transferrin-bound iron's turnover (half-clearance time) is very rapid—typically 60–90 minutes. Because almost all of the iron transported by transferrin is delivered to the erythroid marrow, the clearance time of transferrin-bound iron from the circulation is affected most by the plasma iron level and the erythroid marrow activity. Ferritin is an iron storage protein, and levels represent an indirect measure of total-body iron stores. Free iron, which is toxic to cells, may also be stored intracellularly bound to hemosiderin. Haptoglobin binds free hemoglobin in the plasma, and low levels are consistent with intravascular hemolysis. Albumin, which binds many serum proteins, does not bind signifcant amounts of free iron in plasma.
