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Propionyl-CoA carboxylase catalyses the carboxylation reaction of propionyl-CoA in the mitochondrial matrix. PCC has been classified both as a ligase and a lyase. The enzyme is biotin-dependent. The product of the reaction is -methylmalonyl CoA.
-Methylmalonyl-CoA cannot be directly utilized by animals. It is acted upon by a racemase, yielding -methylmalonyl-CoA, which is then converted into succinyl-CoA by methylmalonyl-CoA mutase. Succinyl-CoA, a Krebs cycle intermediate, is further metabolized into fumarate, then malate, and then oxaloacetate. Oxaloacetate may be transported into the cytosol to form phosphoenol pyruvate and other gluconeogenic intermediates. Propionyl-CoA is therefore an important precursor to glucose.
Propionyl-CoA is the end product of odd-chain fatty acid metabolism, including most methylated fatty acids. The amino acids valine, isoleucine, and methionine are also substrates for propionyl-CoA metabolism.