Methylmalonyl-CoA mutase (EC 188.8.131.52) catalyzes a reversible isomerization between L-methylmalonyl-CoA and succinyl-CoA. The enzyme uses an adenosylcobalamin cofactor. It may be a homodimer, as in mitochondrion, or a heterodimer with partially homologous beta chain that does not bind the adenosylcobalamin cofactor, as in Propionibacterium freudenreichii. The most similar archaeal sequences are separate chains, such as AF2215 and AF2219 of Archaeoglobus fulgidus, that correspond roughly to the first 500 and last 130 residues, respectively of known methylmalonyl-CoA mutases. This model describes the C-terminal domain subfamily. In a neighbor-joining tree (methylaspartate mutase S chain as the outgroup), AF2219 branches with a coenzyme B12-dependent enzyme known not to be 184.108.40.206.