Methylmalonyl-CoA

Diagram of the propionate metabolism pathway, including methylmalonyl-CoA.

Methylmalonyl-CoA is an important intermediate in the metabolism of certain amino acids, odd-chain fatty acids, and cholesterol. It plays a crucial role in the conversion of propionyl-CoA to succinyl-CoA, a process that is essential for the entry of carbon atoms into the citric acid cycle.

Biochemical Pathway

Methylmalonyl-CoA is formed from propionyl-CoA through a carboxylation reaction catalyzed by the enzyme propionyl-CoA carboxylase. This reaction requires biotin as a cofactor and results in the formation of D-methylmalonyl-CoA. The D-methylmalonyl-CoA is then converted to L-methylmalonyl-CoA by the enzyme methylmalonyl-CoA epimerase.

The next step involves the conversion of L-methylmalonyl-CoA to succinyl-CoA by the enzyme methylmalonyl-CoA mutase. This reaction requires adenosylcobalamin, a form of vitamin B12, as a cofactor. Succinyl-CoA can then enter the citric acid cycle, where it is further metabolized to produce energy.

Clinical Significance

Deficiencies in the enzymes involved in the conversion of methylmalonyl-CoA to succinyl-CoA can lead to metabolic disorders such as methylmalonic acidemia. This condition is characterized by the accumulation of methylmalonic acid in the blood, which can lead to metabolic acidosis and other serious health issues.

Vitamin B12 deficiency can also result in elevated levels of methylmalonyl-CoA, as the conversion to succinyl-CoA is impaired. This is often used as a diagnostic marker for vitamin B12 deficiency.

Related Pages

• Propionyl-CoA
• Succinyl-CoA
• Citric acid cycle
• Methylmalonic acidemia
• Vitamin B12