The partially purified enzyme was assayed through the release of tritium from DL-2-hydroxy[2-3H]glutarate in the presence of 2 μM unlabelled D-2-hydroxyglutarate, 50 μM CoCl2 and the indicated concentrations of D-malate (○), mesotartrate (▵), D-lactate (□), L-malate (•), L-tartrate (▴), L-lactate (▪) and D-tartrate (▵).