The subunit structure of methylmalonyl-CoA mutase from Propionibacterium shermanii

5'-Deoxyadenosylcobalamin-dependent methylmalonyl-CoA mutase was purified to homogeneity from Propionibacterium shermanii by a simplified procedure. The native enzyme has an apparent Mr of 165,000, similar to the enzyme from other sources but larger than previously reported. It consists of two non-identical subunits, of Mr 79,000 and 67,000 respectively. The smaller subunit is apparently not a proteolytic fragment of the larger one. The final preparation usually contained some inactive mutase, bearing a tenaciously bound cobalamin species. This protein proved to be readily separable from apoenzyme by fast protein liquid chromatography on anion-exchange columns.