Studies of enzyme-mediated reactions. Part 15. Stereochemical course of the formation of γ-aminobutyric acid (GABA) by decarboxylation of (2S)-glutamic acid with glutamate decarboxylase from Escherichia coli

Abstract

Incubation of (1S)-1-amino[1-³H₁]heptane (1) with the amine oxidase from pea seedlings (EC. 1.4.3.6) results in formation of heptaldehyde with complete removal of tritium showing that the Si-stereospecificity which had already been demonstrated for benzylamine also applies to this aliphatic amine. (2RS)-[2-³H]Glutamic acid is prepared and then decarboxylated with an enzyme from E. coil(E.C. 4.1.1.15) to give γ-amino[4-³H₁]butyric acid (GABA). Hydride reduction of this product gives 4-amino[4-³H₁]butan-1-ol which is shown to have the (4S)-configuration by assay with the pea seedling amine oxidase; this completely removes the tritium from C-4. The decarboxylation of glutamic acid therefore proceeds with retention of configuration.