Heme

Heme is a crucial component of various proteins, including hemoglobin, myoglobin, and cytochromes. It is a complex molecule that contains an iron atom at its center and is responsible for the red color of blood. Heme is essential for life as it plays a vital role in oxygen transport and storage, electron transfer, and drug metabolism.

Structure and Function

Heme is a cyclic compound with four pyrrole rings linked by methine bridges. The iron atom at the center can form two additional bonds, one on either side of the plane of the ring, allowing it to bind to proteins and other molecules.

Heme is a critical part of hemoglobin, the protein in red blood cells that carries oxygen from the lungs to the rest of the body. It is also found in myoglobin, a protein in muscle cells that stores oxygen, and in cytochromes, proteins involved in electron transfer and drug metabolism.

Biosynthesis and Degradation

Heme biosynthesis involves eight enzymatic steps and occurs in both the mitochondria and the cytoplasm of cells. The process begins with the condensation of succinyl-CoA and glycine to form delta-aminolevulinic acid (ALA). The final three steps occur in the mitochondria, where the heme molecule is assembled.

Heme degradation occurs in the liver and spleen, where old or damaged red blood cells are broken down. The process releases iron, which can be reused in the synthesis of new heme molecules, and bilirubin, a waste product excreted in the bile.

Disorders of Heme Metabolism

Disorders of heme metabolism, known as porphyrias, can result in a buildup of heme precursors in the body, leading to a variety of symptoms. These can include skin sensitivity to light, abdominal pain, and neurological problems. Treatment of porphyrias involves managing symptoms and avoiding triggers.

See Also

• Hemoglobin
• Myoglobin
• Cytochromes
• Porphyrias

References

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