Amino Acid Oxidase

Amino acid oxidases, including L-amino acid oxidase (LAAO, EC 1.4.3.2) and D-amino acid oxidase (DAAO, EC 1.4.3.3), are classified as FAD-dependent flavoproteins. They utilize flavin adenine dinucleotide (FAD) as a cofactor to catalyze the oxidative deamination of L- or D-amino acids, producing α-keto acids, ammonia, and hydrogen peroxide.
LAAO is widely found in bacteria, fungi, and mammals, and is primarily involved in antibacterial defense, cytotoxicity, and ecological adaptation. For example, LAAO in snake venom induces apoptosis and inhibits platelet aggregation by generating high local concentrations of hydrogen peroxide, thus enhancing its toxic effects. Microbial LAAOs from species such as Pseudoalteromonas and Aspergillus exhibit potent antibacterial activity and can effectively inhibit the growth of Staphylococcus aureus. In human breast milk, LAAO plays a natural antimicrobial role, helping to prevent mastitis.
In contrast, DAAO is mainly distributed in the liver, kidney, and brain of vertebrates, where it degrades D-amino acids to maintain amino acid homeostasis and regulate neural signaling. In particular, DAAO controls the level of D-serine, a co-agonist of NMDA receptors in the brain. Abnormal DAAO activity has been closely associated with neurodegenerative diseases such as schizophrenia and Alzheimer’s disease. Moreover, the hydrogen peroxide produced by DAAO possesses potential antitumor properties and has been explored for tumor-targeted therapies. DAAO also finds broad applications in the biosynthesis of chiral drugs and in D-amino acid detection^[1][2].