Iron Biochemistry
Plasma iron turnover
The metabolism of iron is dominated by its role in haemoglobin synthesis (Figure 1.2). The plasma iron compartment, within which iron is bound to the transport protein transferrin, is central to this cycle. Iron is transported from the plasma to erythroid precursors in the bone marrow where the synthesis of haemoglobin occurs prior to maturation and release into the circulation. At the end of their 120-day life span, red blood cells (RBC) are degraded by macrophages (RES), mainly in the splenic sinusoids and the iron is removed from the haemoglobin by the enzyme haem oxygenase. A small portion of this iron is stored in macrophages as ferritin or haemosiderin but most is returned to the plasma where it becomes bound to transferrin, thus completing the cycle. In the normal adult male about 20-30 mg of iron passes through via this cycle daily. 1 to 2 mg of iron leaves the plasma daily and enters the liver and other tissues where it is employed for the synthesis of other haem proteins such as cytochromes and myoglobin.
Figure 1.2: The diagrammatic representation of plasma iron turnover. RES (reticuloendothelial system). RBC (red blood cell).
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