Radical enzyme that catalyzes the transformation of methylmalonyl-CoA to succinyl-CoA. Is required for growth on the polyhydroxyalkanoate degradation pathway intermediates 3-hydroxybutyrate and acetoacetate as sole carbon source. (R)-methylmalonyl-CoA = succinyl-CoA Monovalent cations such as NH4(+), Rb(+), Cs(+), K(+), Li(+) or Na(+) are required for enzyme activity. Optimum pH is 7.0. Optimum temperature is 37 degrees Celsius. Metabolic intermediate metabolism; propanoyl-CoA degradation; succinyl-CoA from propanoyl-CoA: step 3/3. Homodimer. Cells lacking this gene show no methylmalonyl-CoA mutase activity, in contrast to wild-type. Belongs to the methylmalonyl-CoA mutase family.