Second unexpected discovery was the production of gaminobutyric
acid (GABA). In other organisms like bacteria,
fungi, mammals, and plants GABA is made from Lglutamate
in a single reaction catalyzed by glutamate
decarboxylase [36], which is missing in the Entamoeba
genome [4]. Thus, amino acid decarboxylases encoded in
the genome may play the equivalent role. Further investigations
of the time kinetics of the changes in various
metabolites indicate that GABA is synthesized by
removal of the acetyl moiety from N-acetylputrescine
(Figure 1). GABA is a major inhibitory neurotransmitter
in the mammalian central nervous system. Role of GABA
during encystation is not clear. However, in Dictyostelium
discoideum, a soil-living ameba, GABA has been shown to
induce terminal differentiation (sporulation) through
GABAB receptor [37]. Further investigations such as
fluxomics using isotopic labeling should unveil the exact
pathway and enzymes involved in the formation of
GABA.