Lead exposure inhibits enzymes involved in which essential process?

• A. Heme synthesis
• B. Glycolysis
• C. Fatty acid oxidation
• D. Protein synthesis

Answer: (A)

Lead exposure blocks enzymes that rely on sulfhydryl groups in the heme biosynthesis pathway, most notably delta-aminolevulinic acid dehydratase and ferrochelatase. By inhibiting these steps, the body’s ability to convert early precursors into heme is impaired, leading to a buildup of upstream intermediates and a shortage of heme. This results in microcytic, hypochromic anemia and characteristic findings like basophilic stippling, since red cells accumulate undegraded ribosomal RNA when heme synthesis is disrupted. The essential consequence is reduced heme availability for hemoglobin and for key cytochromes, which underpins the clinical effects of lead poisoning. While energy pathways like glycolysis or fatty acid oxidation and total protein synthesis can be affected in other contexts, the classic and most direct link to lead’s hematologic effects is inhibition of heme synthesis.