4-Aminobutyric acid

Cortical excitability reflects a balance between excitation and inhibition. Glutamate is the main excitatory and GABA the main inhibitory neurotransmitter in the mammalian cortex. Changes in glutamate and GABA metabolism may play important roles in the control of cortical excitability. Glutamate is the metabolic precursor of GABA, which can be recycled through the tricarboxylic acid cycle to synthesize glutamate. GABA synthesis is unique among neurotransmitters, having two separate isoforms of the rate-controlling enzyme, glutamic acid decarboxylase. The need for two separate genes on two chromosomes to control GABA synthesis is unexplained. Two metabolites of GABA are present in uniquely high concentrations in the human brain. Homocarnosine and pyrrolidinone have a major impact on GABA metabolism in the human brain. Both of these GABA metabolites have anticonvulsant properties and can have a major impact on cortical excitability.

The 4-aminobutyric acid (GABA) is important to produce bio-nylon 4 in biorefineries. First, a glutamate decarboxylase (GAD) was propagated in three different Escherichia coli strains to achieve 100% conversion from 1 M monosodium glutamate after optimization of the process. To make the process greener and more efficient, in situ CO2 adaptation and citrate feeding strategies to maintain the optimal pH value and 498 g/L of GABA was obtained. However, the process releases the equivalent amount of CO2. Therefore, CO2 generated from GABA production was completely sequestered in sodium hydroxide to form bicarbonate and applied in a coupling culture of Chlorella sorokiniana (CS) or Chlorella vulgaris (CV) to increase the biomass when combined with sodium bicarbonate and carbonic anhydrase. Further improvement of 1.65-fold biomass and 1.43-fold lipid content were occurred when supplying GABA to the culture. This integrative process provided the highest GABA production rate without CO2 release, forming an eco-friendly and carbon-neutral technology.