γ-aminobutyric acid (GABA) is a non-protein type of amino acid. It is an inhibitory neurotransmitter in the central nervous system of mammals, crustaceans, and insects. GABA exists widely in human body with the highest concentration in brain nervous system, and minor amount in peripheral tissues and organs such as kidneys, liver and blood vessels. It is also widely found in bacteria, fungi, ferns, and some higher plants. Plants with higher content of GABA are primarily Scrophulariaceae plant rehmannia glutinosa, and Cucurbitaceae, Liliaceae plants.

GABA is a kind of white crystal or crystalline powder. Its chemical name is 4-aminobutyric acid, whose molecular formula is C4H9NO2 with molecular weight of 103.1. Its physical and chemical properties are as following, lobular crystallization (methanol-ethyl ether), needle-like crystals (water-ethanol), pH 6.5~7.5, melting point 197-204℃, Dissociation constants of Ka 3.7×10^-11, Kb 1.7×10^-10 at 25℃, soluble in water, slightly soluble in ethanol, insoluble in organic solvents. GABA decomposes to form pyrrolidinone and water above the melting point. Its molecular structure and model are as follows:

 

Molecular structure of GABA

Molecular model of GABA