Of the eight enzymes of heme biosynthesis, only two are located inside the mitochondrion. Which pair?

• A ALA synthase and ferrochelatase ✓
• B ALA dehydratase and ferrochelatase
• C Uroporphyrinogen decarboxylase and coproporphyrinogen oxidase
• D Porphobilinogen deaminase and ALA synthase

Explanation

The pathway starts in the mitochondrion with ALA synthase, moves into the cytosol for four steps (ALAD through uroporphyrinogen decarboxylase), then returns to the mitochondrion for coproporphyrinogen oxidase, protoporphyrinogen oxidase and finally ferrochelatase, which inserts ferrous iron into protoporphyrin IX. Note that coproporphyrinogen oxidase is also mitochondrial, which eliminates option C. Ferrochelatase deficiency produces erythropoietic protoporphyria.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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