Stereochemistry of Reactions Catalysed by Mammalian‐Brain L‐Glutamate 1‐Carboxy‐lyase and 4‐Aminobutyrate: 2‐Oxoglutarate Aminotransferase

Abstract

Deamination of 4‐aminobutyrate by mammalian or bacterial 4‐aminobutyrate aminotransferases involves the abstraction of the pro‐S hydrogen on C‐4 of 4‐aminobutyrate. Decarboxylation of L‐glutamate by rat brain glutamate decarboxylase occurs with retention of configuration. Inhibition of this enzyme by (S)‐4‐aminohex‐5‐ynoic acid involves the abstraction of the proton at C‐4 of the inhibitor. On the basis of this finding, we postulate the existence of an abnormal reaction of glutamate decarboxylase in which the proton at C‐4 of (S)‐4‐aminohex‐5‐ynoic acid is removed in a manner similar to the one which normally occurs in enzymatic transaminations of L‐amino acids. This reaction is presumably facilitated by the acetylenic group adjacent to the eliminated proton.