The first committed step in the biosynthesis of haem is the condensation of glycine with succinyl CoA to form delta-aminolevulinic acid. This reaction occurs in the mitochondria and is negatively regulated by haem. The reaction pathway then proceeds through a monopyrrole (porphobilinogen), and a linear tetrapyrrole, before formation of the first porphyrin ring structure: uroporphyrinogen III. Modifications of the side chains and saturation of the ring yield first coproporphyrinogen III, then protoporphyrin IX, and finally haem.
Haem is the prosthetic group in a number of proteins, including myoglobin, haemoglobin and cytochrome c.
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