The thiol enzymes ?-aminolevulinic acid dehydratase (ALAD) and ferrochelatase
of this pathway are extremely sensitive to lead.
Pb inhibits the insertion of iron into protoporphyrin by ferrochelatase
, possibly through binding of Pb to the vicinal sulphhydryl groups of the active site or indirectly through disruption of mitochondrial structure.
(an iron-sulfur enzyme) catalyzes the last step in heme biosynthesis by inserting iron into protoporphyrin IX to produce heme (Ponka, 1999; Atamna, 2004).
The condition is caused by a deficiency of ferrochelatase
, which leads to accumulation of protoporphyrin IX.
Lead is a potent inhibitor of [delta]-aminolevulinic acid dehydratase (ALAD), coproporphyrinogen oxidase, and ferrochelatase
, enzymes that catalyze the second, sixth, and final steps, respectively, in the biosynthesis of heme (Onalaja and Claudio 2000; Warren et al.
One DMR was within the intronic region of the ferrochelatase
(FECH)  gene on chromosome 18.
Erythropoietic protoporphyria (EPP) is a disease associated with a diminished activity of ferrochelatase
(FECH) (EC.188.8.131.52), the final enzyme of heme biosynthesis that catalyzes the conversion of protoporphyrin (PROTO IX) into heme [1, 2].
Lead may inhibit the body's ability to make hemoglobin by interfering with several enzymatic steps in the heme pathway, through inhibiting aminolevulinic acid dehydratase and ferrochelatase
Apart from this, lead also decreases the activity of ferrochelatase
, the last step of heme synthesis.
Pb also interferes with the normal functioning of the intramitochondrial enzyme ferrochelatase
, which is responsible for the chelation of iron by protoporphyrin.
(d) A and E, PBGD; B, ferrochelatase
; C, UROD; D, PBGD/UROD/coproporphyrinogen oxidase/protoporphyrinogen oxidase.
Formation of zinc protoporphyrin in cultured hepatocytes: effects of ferrochelatase
inhibition, iron chelation or lead.