Private Flashcard From Lippincott's - Ch. 21
What happens when porphyrins production exceeds the availability of the apoproteins that require it?
Heme accumulates and is converted to hemin by the oxidation of Fe2+ to Fe3+. Hemin decreases the activity of hepatic ALAS1 by causing decreased synthesis of the enzyme, through inhibition of mRNA synthesis and use (heme decreases stability of the mRNA), and by inhibiting mitochondrial import of the enzyme.