D-amino acid oxidase (DAO),with MW of 39 kDa,is a flavoprotein which uses flavin adenine dinucleotide as its prosthetic group. Its substrates include a wide variety of D-amino acids,but it is inactive on the naturally occurring L-amino acids. DAO may play a role in the pathophysiology of schizophrenia and act as a detoxifying agent which removes D-amino acids that accumulate during aging.