Abstract
D-Amino acid oxidase (DAO) is a flavin enzyme that catalyzes the oxidative deamination of d-amino acids. This enzyme has been studied extensively both biochemically and structurally as a model for the oxidase-dehydrogenase class of flavoproteins. This enzyme also has various applications, such as the determination of d-amino acids and production of building blocks for a number of pharmaceuticals. DAO has been found mainly in eukaryotic organisms and has been suggested to play a significant role in various cellular processes, one of which includes neurotransmission in the human brain. In contrast, this enzyme has not been identified in prokaryotic organisms. Some studies have recently identified and characterized DAO enzyme in some actinobacteria. In addition, a genome database search reveals a wide distribution of DAO homologous genes in this bacterial group. The bacterial DAOs characterized so far have certain distinct properties in comparison to eukaryotic DAOs. These enzymes also exhibit some important applicable properties, suggesting that bacteria could be used as a source for obtaining novel and useful DAOs. The physiological function of bacterial DAO have been proposed to include the degradation of non-canonical d-amino acids released from cell wall, but is still largely unknown and need to be studied in depth.