Radical enzyme that catalyzes the transformation of (2R)-ethylmalonyl-CoA to (2S)-methylsuccinyl-CoA (PubMed:25448820). Is involved in the ethylmalonyl-CoA pathway for acetyl-CoA assimilation required for M.extorquens growth on one- and two-carbon compounds such as ethylamine, methanol or ethanol as sole carbon source (PubMed:8868443, PubMed:8704985, PubMed:25448820). This enzyme acts as a regulatory metabolic control point in this pathway, that allows M.extorquens to efficiently restore metabolic balance when challenged with a sudden change in the growth substrate (PubMed:25448820). (2R)-ethylmalonyl-CoA = (2S)-methylsuccinyl-CoA Up-regulated during growth on ethylamine. Cells lacking this gene lose the ability to grow on C1 (methanol and methylamine) and C2 (ethanol and ethylamine) compounds, and also on beta-hydroxybutyrate, but they grow normally on pyruvate. Growth on C1 and C2 compounds is restored by addition of glyoxylate or glycolate, indicating that these mutants are unable to convert acetyl-CoA into glyoxylate. Belongs to the methylmalonyl-CoA mutase family.