Heme biosynthesis pathway showing chemical intermediates and sites of production (mitochondria versus cytosol)
Heme synthesis begins with the formation of delta-aminolevulinic acid (ALA) from glycine and succinyl-CoA by ALA synthase (ALAS); this step is rate-limiting in the liver. Hepatic ALAS is mainly regulated by heme via feedback repression (dashed arrow at the top of the frame). Refer to UpToDate for a discussion of porphyrias that result from deficiencies of these enzymes.
Reproduced from: Anderson KE. The porphyrias. In: Zakim and Boyer's Hepatology: A Textbook of Liver Disease, 5th ed, Boyer TD, Wright TL, Manns MP, Zakim D (Eds), Elsevier, Philadelphia 2006. Illustration used with the permission of Elsevier Inc. All rights reserved.
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