Which enzymes are inhibited by lead?

• A. ALA dehydratase and succinate dehydrogenase
• B. Ferrochelatase and ALA dehydratase
• C. Uroporphyrinogen decarboxylase and porphobilinogen synthase
• D. Heme oxygenase and ferrochelatase

Answer: (B)

Lead is a well-known environmental toxin that interferes with several enzymatic processes in the body, particularly those involved in heme synthesis. The correct answer identifies two key enzymes that are inhibited by lead: ferrochelatase and ALA dehydratase.

Ferrochelatase is responsible for catalyzing the final step in heme synthesis, which involves the insertion of iron into protoporphyrin IX to form heme. Inhibition of this enzyme can lead to an accumulation of protoporphyrin and a reduction in the production of hemoglobin, resulting in anemia.

ALA dehydratase, on the other hand, plays a crucial role early in the heme synthesis pathway by catalyzing the condensation of two molecules of delta-aminolevulinic acid (ALA) to form porphobilinogen. The inhibition of this enzyme by lead results in the accumulation of ALA, which is a neurotoxin and contributes to the neurological symptoms associated with lead poisoning.

The combination of inhibiting these two enzymes disrupts the normal production of heme, leading to various clinical manifestations, including anemia and neurological impairment, which are hallmark features of lead poisoning.