iron

How does the body regulate the amount of iron? Fortunately, most of us are able to maintain appropriate levels of available iron in the body (enough available iron to ensure an adequate supply of hemoglobin, but not so much as to produce toxic effects), even if our iron consumption does not always exactly match the body's iron loss. Ferritin (Figure 1) is the key to this important control of the amount of iron available to the body. Ferritin is a protein that stores iron and releases it in a controlled fashion. Hence, the body has a "buffer" against iron deficiency (if the blood has too little iron, ferritin can release more) and, to a lesser extent, iron overload (if the blood and tissues of the body have too much iron, ferritin can help to store the excess iron).

How does ferritin store iron? Ferritin has the shape of a hollow sphere. Inside the sphere, iron is stored in the Fe(III) oxidation state. It is incorporated in the mineral ferrihydrite, [FeO(OH)]8[FeO(H2PO4)], which is attached to the inner wall of the sphere. To release iron when the body needs it, the iron must be changed from the Fe(III) to the Fe(II) oxidation state. Then, the iron leaves through channels in the spherical structure. Thus, the structure of ferritin is extremely important for the protein's ability to store and release iron in a controlled fashion. In order to understand how ferritin helps to maintain the correct amount of available iron in the body, we must study the protein's structure in detail.