Improvement in thermal stability and substrate binding of pig kidney d-amino acid oxidase by chemical modification

Chemical modification was evaluated to stabilize pig kidney d-amino acid oxidase (pkDAAO), which is required for analytical determination of d-amino acids. Optimization of modification conditions was performed to obtain high recovery yield and stability, and chemical modification at 30°C for 12 h with a highly concentrated enzyme solution gave dextran-conjugated pkDAAO with a 70% yield of activity. pkDAAO was stable at less than 55°C at pH 6.0, while the conjugated enzyme was stable even at 70°C. In addition, the conjugated enzyme showed decreased Km values for d-amino acids. Because of these outstanding charcteristics, this new material is expected to be available for use as a liquid assay reagent.