Activity of yeast d-amino acid oxidase on aromatic unnatural amino acids

d-Amino acid oxidase is a FAD-dependent enzyme that catalyses the conversion of the d-enantiomer of amino acids into the corresponding α-keto acid. Substrate specificity of the enzyme from the yeast Rhodotorula gracilis was investigated towards aromatic amino acids, and particularly synthetic α-amino acids. A significant improvement of the activity (Vmax,app) and of the specificity constant (the Vmax,app/Km,app ratio) on a number of the substrates tested was obtained using a single-point mutant enzyme designed by a rational approach. With R. gracilis d-amino acid oxidase the complete resolution of d,l-homo-phenylalanine was obtained with the aim to produce the corresponding pure l-isomer and to use the corresponding α-keto acid as a precursor of the amino acid in the l-form.