Conversion of propionyl-CoA in succinyl CoA

The major precursors are indicated with their approximated contribution to whole body propionate metabolism in the fasting state. Propionyl-CoA is converted into D-methylmalonyl-CoA by the action of the biotin-dependent enzyme, propionyl-CoA carboxylase. The product is racemized into L-methylmalonyl-CoA and isomerized into succinyl-CoA, a Krebs cycle intermediate. The L-methylmalonyl-CoA mutase reaction requires adenosylcobalamin, an activated form of vitamin B12. The position of the MMAA and MMAB gene products, which harbor mutations in cblA and cblB MMA, are depicted along the pathway of intramitochondrial cobalamin metabolism. The nature of the lesion in cblH and cblD variant 2 deficiencies is uncertain (Stucki et al 2012). All limit the activity of the L-methylmalonyl-CoA enzyme. (Contributed by Dr. Gerard Berry.)