Define Transport and Storage of Iron?
You have seen that transferrin binds both newly absorbed iron and iron released after degradation of haemoglobin. Transferrin is a glycoprotein and has two binding sites for Fe3+. It acts as an iron transport protein. Normally, in plasma it is one-third saturated with ferric ions. It distributes iron throughout the body to wherever it is needed, mostly to eiythrocyte precursors in the bone marrow. In iron deficiency, transferrin saturation is reduced while in iron overload, tansferrin saturation gets increased.
Any absorbed iron in excess of body needs is stored in the liver, in two forms, as ferritin and hnemosiderin. Ferritin and haemosiderin are the two major iron storage proteins. The ratio of these two proteins in the liver varies according to the level of iron stored, with fenitin predominating at lower iron concentrations and haemosiderin at higher concentrations. Iron is released from these stores in times of need more readily from feiritin than haemosiderin. Binding of iron by protein during storage and transport serves as a defense mechanism. How? If iron ions are left unbound, the redox activity of iron can lead to the generation of harmful free radicals that can cause damage to the cells and their membranes. We have been reading that once iron is absorbed our body tries to use it conservatively and re-utilizes it again and again. What would happen then, if iron is consumed in excess of our requirements? Further, the iron absorption need not always be complete. Unabsorbed iron would get excreted. Let us read how iron gets excreted from the body.