Biological relevance

Formation of the haptoglobin-haemoglobin complex plays an important role in iron metabolism by contributing towards the  recycling and storage of iron found in haem groups on haemoblogin. Iron is usually recycled and stored in liver and spleen cells. Research has shown that lack of haptoglobin leads to accumulation of iron in the kidney⁴. This eventually damages the kidney cells, as they are not designed to store iron. Another important function of the complex - which has been discussed briefly in previous sections - is the reduction of oxidative damage by αβHb dimers. Although haptoglobin prevents haem groups from causing damage, it does not alter their reactive properties. Radical intermediates can form on the surface of the protein, which can oxidise lipids and cause structural changes. There are several residues that are particularly vulnerable to oxidative modification by hydrogen peroxide, however, these are buried at the interface of the two proteins of the complex. Haptoglobin binding shields these residues and, since it binds close to the haem group, may also stabilise the protein in this region, preventing haem release. This tight, almost irreversible interaction is vital for protecting the body from damage by haemoglobin, therefore has great clinical relevance. For example, haptoglobin levels in blood can be used as a marker of hemolytic anaemia and other similar diseases.