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Walk the Even Hospital Database by book and chapter — the raw source passages that ground Ask, DDx, and the rest.
2 passages
Heme is a porphyrin ring complexed with ferrous iron and protoporphyrin IX. Heme is an essential prosthetic group in proteins that is necessary as a subcellular compartment to perform diverse biological functions like hemoglobin and myoglobin.[1] Other enzymes which use heme as a prosthetic group includes cytochromes of the electron transport chain, catalase, and nitric oxide synthase. The major tissues for heme synthesis are bone marrow by erythrocytes and the liver by hepatocytes.
A defect or mutation in 5’- aminolevulinic acid synthase 2 (ALAS2) leads to a disorder called X-linked sideroblastic anemia. It reduces protoporphyrin production and decreases heme. However, Iron continues to enter the erythroblast leading to an accumulation in the mitochondria and therefore a manifestation of the disease. During the biosynthetic pathway, the linear hydroxymethylbilane can spontaneously form a “faulty” porphyrin ring when not immediately used as a substrate for uroporphyrinogen synthesis. If uroporphyrinogen III synthase is deficient, then hydroxymethylbilane spontaneously closes and forms a different molecule called uroporphyrinogen I. Uroporphyrinogen leads to the formation of coproporphyrinogen I. This molecule does not result in the formation of heme.