Propionic acidemia results from propionyl-CoA carboxylase deficiency. This enzyme uses biotin and converts propionyl-CoA to methylmalonyl-CoA. A separate patient has methylmalonic acidemia due to methylmalonyl-CoA mutase deficiency. Both patients accumulate odd-chain fatty acids in their tissues. Propionic acid is also produced from the catabolism of which four amino acids?

• A Isoleucine, valine, threonine, methionine ✓
• B Leucine, lysine, phenylalanine, tyrosine
• C Isoleucine, leucine, valine, alanine
• D Threonine, serine, glycine, alanine

Explanation

Propionyl-CoA is generated from the catabolism of odd-chain fatty acids and four amino acids: isoleucine (via propionyl-CoA after 2-methylbutyryl-CoA conversion), valine (via isobutyryl-CoA pathway ending in methylmalonyl-CoA/propionyl-CoA), threonine (via alpha-ketobutyrate → propionyl-CoA), and methionine (via alpha-ketobutyrate as well). Together these are remembered as 'IVTM' — Isoleucine, Valine, Threonine, Methionine. Leucine and lysine are purely ketogenic. This is why patients with propionic acidemia or methylmalonic acidemia are placed on protein-restricted diets specifically low in these four amino acids while ensuring adequate leucine and lysine intake, which are not propionogenic.

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

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Written and medically reviewed by the StethoPrep medical team.