Propionyl-CoA carboxylase catalyses the carboxylation reaction of propionyl CoA in the mitochondrial matrix. The enzyme is biotin-dependent. The product of the reaction is (S)-methylmalonyl CoA. Propionyl CoA is the end product of metabolism of odd-chain fatty acids, and is also a metabolite of most methyl-branched fatty acids. It is also the main metabolite of valine, and together with acetyl-CoA, is a metabolite of isoleucine, as well as a methionine metabolite. Propionyl-CoA is thus of great importance as a glucose precursor. (S)-Methylmalonyl-CoA is not directly utilizable by animals; it is acted on by a racemase to give (R)-methylmalonyl-CoA. The latter is converted by methylmalonyl-CoA mutase (one of a very few Vitamin B₁₂-dependent enzymes) to give succinyl-CoA. The latter is converted to oxaloacetate and then malate in the Krebs cycle. Export of malate into the cytosol leads to formation of oxaloacetate, phosphoenol pyruvate, and other gluconeogenic intermediates.