Mechanism of action of coenzyme B12. Hydrogen transfer in the isomerization of .beta.-methylaspartate to glutamate

Use of a mixture of unlabeled and tetradeuterio-,Bmethylaspartate coenzyme B_(12) dependent β-methylaspartate-glutamate mutase has shown that the hydrogen that becomes one of three equivalent hydrogens during isomerization. Kinetic isotope effects suggest that cleavage the bond in the substrate from carbon to that hydrogen which migrates is an important component of the rate-determining . The evidence also supports the existence of an which can partition with similar probabilities β-methylaspartate or to glutamate. Mechanistic implications these findings are discussed.