GABA is primarily formed
by the irreversible α-decarboxylation reaction of L-glutamic acid
or its salts, catalysed by glutamic acid decarboxylase enzyme
(GAD; EC 4.1.1.15) (Fig. 1) (Satya Narayan & Nair, 1990) whose
biochemical properties have been characterized (Nomura,
Nakajima, Fujita, & Kobayashi, 1999).