Methylmalonic acid

Diagram of the propionate pathway, showing the role of methylmalonic acid.

Methylmalonic acid (MMA) is a dicarboxylic acid that is a key intermediate in the metabolism of certain amino acids and lipids. It is a structural isomer of succinic acid and plays a crucial role in the propionate pathway, which is important for the metabolism of odd-chain fatty acids and certain amino acids such as valine, isoleucine, methionine, and threonine.

Biochemical Role

Methylmalonic acid is involved in the conversion of propionyl-CoA to succinyl-CoA, a critical step in the citric acid cycle. This conversion requires the enzyme methylmalonyl-CoA mutase, which is dependent on vitamin B12 (cobalamin) as a cofactor. In the absence of adequate vitamin B12, methylmalonic acid accumulates in the blood, leading to a condition known as methylmalonic acidemia.

Clinical Significance

Elevated levels of methylmalonic acid in the blood or urine can be indicative of vitamin B12 deficiency, which can lead to megaloblastic anemia and neurological disorders. Methylmalonic acidemia is a metabolic disorder that can result from genetic defects in the enzymes involved in the conversion of methylmalonyl-CoA to succinyl-CoA. This condition can lead to severe metabolic acidosis, developmental delays, and other serious health issues.

Diagnostic Use

The measurement of methylmalonic acid levels is used as a diagnostic tool to assess vitamin B12 status. Elevated levels of MMA are often used to confirm a diagnosis of vitamin B12 deficiency, especially in cases where serum vitamin B12 levels are borderline or normal.

Related Pathways

Methylmalonic acid is part of the broader propionate metabolism pathway. This pathway is essential for the breakdown of odd-chain fatty acids and certain amino acids, ultimately feeding into the citric acid cycle for energy production.

Related Pages

• Vitamin B12
• Methylmalonyl-CoA mutase
• Propionate metabolism
• Methylmalonic acidemia
• Citric acid cycle