DAAO reaction mechanism

First the D-amino acid substrate in the catalytic center is dehydrogenated by the FAD cofactor yielding the corresponding iminoacid. In the next step the resulting reduced FADH⁻ is reoxidized by electron transfer to O₂. The activated oxygen eventually forms H₂O₂ and is released. Finally, the iminoacid intermediate hydrolyzes and the keto acid product is released along with ammonium. In order to facilitate the flavin reoxidation oxygen has to get close to flavin which is located deep inside the binding pocket. O₂ supposedly reaches the catalytic site through a special access channel.

Fig 1: DAAO reaction scheme: Amino acid oxidation by hydride transfer to FAD; flavin reoxidation by electron transfer to O₂; H₂O₂ release; product hydrolyzation and release.