Which compounds condense to form aminolevulinic acid?

Which compounds condense to form aminolevulinic acid?

• A. Oxoglutarate and aspartate
• B. Isocitrate and coenzyme II
• C. Oxaloacetate and malate
• D. Succinyl coenzyme A and glycine

Answer: (D)

Aminolevulinic acid is made early in heme biosynthesis by a single condensation reaction in the mitochondria. The enzyme responsible, ALA synthase, combines glycine with the succinyl group of succinyl-CoA, releasing CoA and carbon dioxide to form aminolevulinic acid. This specific pairing—glycine with succinyl-CoA—is unique to this step, which is why it is the correct choice. The other pairings involve intermediates or reactions from general metabolism (transamination and various TCA cycle steps) and do not produce aminolevulinic acid. For example, interactions like oxoglutarate with aspartate relate to amino transfer reactions, and combinations such as oxaloacetate with malate are tied to other carbon–carbon rearrangements in metabolism, not ALA formation.

Aminolevulinic acid is made early in heme biosynthesis by a single condensation reaction in the mitochondria. The enzyme responsible, ALA synthase, combines glycine with the succinyl group of succinyl-CoA, releasing CoA and carbon dioxide to form aminolevulinic acid. This specific pairing—glycine with succinyl-CoA—is unique to this step, which is why it is the correct choice.

The other pairings involve intermediates or reactions from general metabolism (transamination and various TCA cycle steps) and do not produce aminolevulinic acid. For example, interactions like oxoglutarate with aspartate relate to amino transfer reactions, and combinations such as oxaloacetate with malate are tied to other carbon–carbon rearrangements in metabolism, not ALA formation.