D-Amino Acid Oxidase

Abstract

Abstract A recently described spectrophotometric assay for d-amino acid oxidase was used to study the inhibition of the enzyme by a series of adenine and flavin derivatives. AMP, ADP, and ADP-ribose inhibited the enzyme competitively with respect to FAD. No instantaneous inhibition was observed with flavin derivatives. These inhibition studies indicated that the adenosine moiety and the pyrophosphate group of the FAD molecule contributed to the effective binding of FAD to d-amino acid oxidase. The isoalloxazine moiety of FAD appears to be less tightly bound than the adenosine moiety. FMN and riboflavin were found to inactivate the d-amino acid oxidase apoenzyme by a time-dependent photochemical process. This photoinactivation of the enzyme in the presence of flavin derivatives is enhanced by the adenine compounds. The various forms of d-amino acid oxidase were studied by gel filtration. This technique indicated that the apoenzyme form and holoenzyme form each have a molecular weight of approximately 50,000. This value corresponds to the minimum molecular weight calculated per FAD-binding site. The benzoate complex at low protein concentrations was found to contain a 50,000 molecular weight species and a 100,000 molecular weight species. At higher concentrations, the benzoate complex was found to exist entirely as the dimer.