On the steric course of the adenosylcobalamin-dependent 2-methyleneglutarate mutase reaction in Clostridium barkeri.

The enzymatically active enantiomer of 3-methylitaconate in Clostridium barkeri has (R)-configuration. This was checked by fermentation of the racemate and reisolation of the (S)-enantiomer. In addition (R)-3-methylitaconate was synthesized by enzymatic isomerisation of 2,3-dimethylmaleate which was protonated at the Si-face. 2-Methylene[2-2H1]glutarate was synthesized via (R)-3-methyl[3-2H1]itaconate by brief incubation of 2,3-dimethylmaleate with a cell-free extract of Clostridium barkeri in 2H2O. The predominantly monodeuterated compound was oxidized to (S)-[2-2H1]succinate as analysed by circular dichroism. The results demonstrate that 2-methyleneglutarate mutase catalyses the reversible migration of an acryloyl residue from the alpha-carbon to the beta-carbon of propionate with inversion of configuration at the alpha-carbon.