Amino Acid Oxidase, D-

D-Amino acid oxidase (DAO) in the presence of molecular oxygen oxidatively deaminates D-amino acids to corresponding [[alpha]]-keto acids:

DAO is a flavoprotein oxidase, flavin being the only prosthetic group. The enzyme from hog kidney has been extensively studied. It is isolated as a stable crystalline complex with benzoate, from which the holo and apoenzyme may be prepared. The benzoate is readily exchanged for a substrate. See Yagi (1971) and the review by Bright and Porter (1975).

Purification procedures have been published by Curti et al. (1973) and Tu et al. (1973).

Characteristics of D-Amino Acid Oxidase from Hog Kidney:

Molecular weight: Monomeric MW: 38,000-39,000 (Curti et al. 1973; Tu et al. 1973).

Composition: DAO undergoes a concentration-dependent dimerization. Each monomer contains one mole of FAD. The amino acid concentration has been determined by Curti et al. (1973). They report 5 sulfhydrl groups and 8 tryptophans per mole FAD. The ratio A₂₇₄/A₄₆₈=9.5. Tu and McCormick (1973) indicate that cysteine and tyrosine residues are probably involved in the active site. Yagi et al. (1973) report the monomer more active than the dimer.

Optimum pH: Dependent upon substrate: approximately pH 9 for D-alanine (Dixon and Kleppe 1965c).

Specificity: The D isomers of proline, methionine, isoleucine, alanine, valine and phenylalanine are good substrates (Scannone et al. 1964; Dixon and Kleppe 1965b). The enzyme is reported to act on L-proline (Wellner and Scannone 1964) and D-lactate (Yagi and Ozawa 1964b). The reaction between D-lysine and the enzyme is reported by Yagi et al. (1969a). See Konno and Yasumura (1992).

Stability: The enzyme is stable for months at room temperature as a dry, lyophilized powder and in solution at high protein concentration when refrigerated. 1.4 X 10^-5 M FAD prevents loss of activity upon dilution (Dixon and Kleppe 1965a).