Binding Aspects of D-Amino-Acid Oxidase With Various Carboxylic Acids

Abstract

The binding aspects of D-amino-acid oxidase [EC 1. 4. 3. 3, D-amino acid: oxygen oxidoreductase (deaminating)] with various carboxylic acids have been investigated in terms of changes in the absorption spectrum of its coenzyme, FAD, and in ORD and CD spectra in the wavelength range of 300-600 mμ, upon the formation of the enzyme-carboxylate complexes. Interaction of the enzyme with various inhibitor carboxylic acids seemed to involve hydrophobic bonding between alkyl group of the carboxylic acid and hydrophobic area of the enzyme. The strength of the binding is affected by the size of alkyl group of the carboxylate. This may be an indication of the local structure of the binding site of this enzyme molecule.
The results of the study on the complexes of the enzyme with aminobenzoates indicate the binding between the enzyme and the acids via a nitrogen atom close to the carboxylate group, suggesting the participation of the nitrogen lone-pair in forming the intermolecular charge-transfer complex with the enzyme.