ñ-Aminobutyric acid (AABA), also known as homoalanine in biochemistry, is a non-proteinogenic alpha amino acid with chemical formula C<sub>4</sub>H<sub>9</sub>NO<sub>2</sub>. The straight two carbon side chain is one carbon longer than alanine, hence the prefix homo-. The conjugate base of ñ-aminobutyric acid is the carboxylate ñ-aminobutyrate.
Homoalanine is biosynthesized by transaminating oxobutyrate, a metabolite in isoleucine biosynthesis. It is used by nonribosomal peptide synthases. One example of a nonribosomal peptide containing homoalanine is ophthalmic acid, which was first isolated from calf lens.
ñ-Aminobutyric acid is one of the three isomers of aminobutyric acid. The two other are the neurotransmitter ó-aminobutyric acid (GABA) and ò-aminobutyric acid (BABA) which is known for inducing plant disease resistance.
This amino acid has been detected in meteorites.