Which of the following represents the enzyme of porphyrin biosynthesis whose activity is negatively affected by hemin?

Question

Quizplus · Accepted Answer

Hemin negatively regulates d-aminolevulinic acid synthase (ALA synthase), which is the rate-limiting enzyme in porphyrin biosynthesis.  The enzyme ALA synthase is the rate-limiting enzyme of heme biosynthesis. In hepatocytes, heme is required for incorporation into the cytochromes, in particular, the P450 class of cytochromes that are important for detoxification. In addition, numerous cytochromes of the oxidative-phosphorylation pathway contain heme. The Fe3+ oxidation product of heme is termed hemin. Hemin acts as a feedback inhibitor on ALA synthase. Hemin also inhibits transport of ALA synthase from the cytosol (its site of synthesis) into the mitochondria (its site of action), as well as represses synthesis of the enzyme.

Which of the Following Represents the Enzyme of Porphyrin Biosynthesis