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

1 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 2‐Methylene[2‐ 2 H 1 ]glutarate was synthesized via ( R )‐3‐methyl[3‐ 2 H 1 ]itaconate by brief incubation of 2,3‐dimethylmaleate with a cell‐free extract of Clostridium barkeri in 2 H 2 O. The predominantly monodeuterated compound was oxidized to ( S )‐[2‐ 2 H 1 ]succinate as analysed by circular dichroism. The results demonstrate that 2‐methyleneglutarate mutase catalyses the reversible migration of an acryloyl residue from the α‐carbon to the β‐carbon of propionate with inversion of configuration at the α‐carbon.