The flavoenzyme d-amino acid oxidase from Rhodotorula gracilisis a homodimeric protein whose dimeric state has been proposed to occur as a result of (a) the electrostatic interactions between positively charged resi-dues of thebF5–bF6 loop of one monomer and negatively charged residues belonging to thea-helices I3¢ and I3¢¢ of the other monomer, and (b) the interaction of residues (. Trp243) belonging to the two monomers at the mixed interface region.