Propionyl-CoA to succinyl-CoA metabolic pathway (PCC/MCEE/MUT pathway)

The Propionyl-CoA to succinyl-CoA metabolic pathway is a critical mitochondrial multi-enzyme sequence responsible for the catabolism of odd-chain fatty acids, cholesterol, and branched-chain amino acids such as valine and isoleucine (UniProt P05165, P22033). It consists of three primary enzymes: Propionyl-CoA carboxylase (PCC), Methylmalonyl-CoA epimerase (MCEE), and Methylmalonyl-CoA mutase (MUT). PCC initiates the pathway by converting propionyl-CoA to D-methylmalonyl-CoA using biotin as a cofactor, while MUT completes the process by converting L-methylmalonyl-CoA to the TCA cycle intermediate succinyl-CoA using adenosylcobalamin (StatPearls, PMID: 30725911). Genetic deficiencies in these enzymes lead to Propionic Acidemia and Methylmalonic Acidemia, characterized by life-threatening metabolic acidosis and hyperammonemia (NIH GARD). Therapeutic interventions include cofactor supplementation (biotin, vitamin B12), carnitine to facilitate metabolite excretion, and emerging mRNA therapies like mRNA-3927 and mRNA-3705 designed to restore intracellular enzyme levels (Moderna, 2024). This pathway is a major focus for metabolic medicine due to the high morbidity associated with its dysfunction.

Other names

Propionate catabolic pathwayPropionyl-CoA carboxylase complexMethylmalonyl-CoA mutase complexPCCMCEEMUTMMUT

The primary mechanisms include cofactor supplementation (biotin for PCC, vitamin B12 for MUT) to maximize residual enzyme activity, carnitine-mediated conjugation of toxic acyl-CoA intermediates for urinary excretion, and mRNA-based delivery of functional transcripts to restore protein expression in the liver (StatPearls, Moderna 2024).