Haem

Haem or heme is a component of hemoglobin, the molecule in red blood cells that carries oxygen from the lungs to the body's tissues and returns carbon dioxide from the tissues back to the lungs.

Structure

Haem is a porphyrin containing an iron atom. The iron atom, usually in the ferrous state (Fe2+), is coordinated to four nitrogens of the porphyrin. It can either be in a fifth coordination site or a sixth, which is either occupied by a coordinated water molecule (in the case of myoglobin) or a histidine residue of the protein (in the case of hemoglobin). The sixth coordination site is the place where oxygen binds.

Function

Haem is essential for life in most organisms. It is used in cytochromes, proteins that mediate electron transport. Haem proteins are also found in the mitochondria, the powerhouses of the cell.

Health implications

Defects in the biosynthesis of haem can lead to several human diseases, including porphyria and sideroblastic anemia. In addition, the breakdown of haem can lead to the formation of bilirubin, which can cause jaundice if not properly processed by the body.

See also

• Hemoglobin
• Red blood cells
• Oxygen
• Carbon dioxide
• Iron
• Porphyrin
• Cytochromes
• Mitochondria
• Porphyria
• Sideroblastic anemia
• Bilirubin
• Jaundice

Haem Resources
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