1. Intermediates in the biosynthesis of heme, as follows: four porphobilinogens condense to form uroporphyrinogens I and III (giving rise to side products uroporphyrins I and III) that are decarboxylated to form coproporphyrinogens I and III (giving rise to side products coproporphyrins I and III); coproporphyrinogen III is oxidized to protoporphyrinogen III (IX), which is then oxidized to form protoporphyrin III (IX) (this last intermediate adds ferrous iron to yield heme); certain porphyrinogens are elevated in certain porphyrias.
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