Influence of Met/Leu amino acid changes on catalytic properties and oxidative and thermal stability of yeast D-amino acid oxidase

Abstract

The oxidative stability of enzymes is mostly dependent on the stability of the Cys and Met residues. Three single point mutants with Met/Leu substitutions in D-amino acid oxidase (DAAO, EC 1.4.3.3) from the yeast Trigonopsis variabilis (TvDAAO) are prepared and characterized. The positions for the amino acid residue substitutions are selected based on multiple alignment of different DAAO amino acid sequences and analysis of the three-dimensional structure of TvDAAO. It is shown that the substrate specificity profile ischanged for all of the mutants. The K_M values for the small and bulky D-amino acidsare increased and decreased, respectively. One of the Met/Leu substitutions results in a two- to threefold increase in thermal stability as compared to the wild-type enzyme. A method for the determination of TvDAAO stability in the presence of hydrogen peroxide is developed and the oxidative stability of wild-type and mutant TvDAAOs is studied. It is shown that none of thethree mutations changes the oxidative stability of the enzymes.