Before revision: Definition by negation 260px|Lysine Technically, any organic compound with an amine (–NH2) and a carboxylic acid (–COOH) functional group is an amino acid.
After revision: might be important neurotransmiters, such as γ-Aminobutyric acid (Gaba)Definition by negation 260px|Lysine Technically, any organic compound with an amine (–NH2) and a carboxylic acid (–COOH) functional group is an amino acid.