“DFT and ONIOM(DFT:MM) Studies on Co-C Bond Cleavage and Hydrogen Transfer in B12-Dependent Methylmalonyl-CoA Mutase. Stepwise or Concerted Mechanism?” Xin Li, Lung Wa Chung, Piotr Paneth and Keiji Morokuma, J. Am. Chem. Soc. 131, 5115-5125 (2009)