Iron is transpoed bound to: September 2011

Ans. B: Transferrin Transferrin/siderophilin binds the iron in the lumen of GIT and most of the iron is transpoed bound to this globulin across the mucosal brush border Transferrin They are iron-binding blood plasma glycoproteins that control the level of free iron in biological fluids. In humans, it is encoded by the TF gene. Transferrin is a glycoprotein that binds iron very tightly but reversibly. Although iron bound to transferrin is less than 0.1% (4 mg) of the total body iron, it is the most impoant iron pool, with the highest rate of turnover. Transferrin has a molecular weight of around 80 kDa and contains 2 specific high-affinity Fe (III) binding sites. The affinity of transferrin for Fe (III) is extremely high but decreases progressively with decreasing pH below neutrality. When not bound to iron, it is known as "apo-transferrin" Ferritin It is a ubiquitous intracellular protein that stores iron and releases it in a controlled fashion. The amount of ferritin stored reflects the amount of iron stored. In humans, it acts as a buffer against iron deficiency and iron overload. Ferritin is a globular protein complex consisting of 24 protein subunits and is the primary intracellular iron-storage protein in both prokaryotes and eukaryotes, keeping iron in a soluble and non-toxic form. Ferritin that is not combined with iron is called apoferritin.