Assays of d-amino acid oxidases

Abstract

d-Amino acid oxidase and d-aspartate oxidase are two well-known FAD-containing flavooxidases that catalyze the same reaction (the oxidative deamination) on different d-amino acids. d-aspartate oxidase is specific for acidic d-amino acids (i.e., d-aspartate and d-glutamate) and d-amino acid oxidase is active on neutral and polar d-amino acids (a low activity is also detected on basic d-amino acids). The assay of these flavoenzymes is of utmost importance in different fields because d-amino acids are common constituents of bacterial cell walls, are present in foods and because free d-serine and d-aspartic acid were identified in brain and peripheral tissues of mammals. In this chapter, we report on the most used methods employed to assay the activity of d-amino acid oxidase and d-aspartate oxidase. Interestingly, their activity can be followed using different assays, namely d-amino acid or oxygen consumption, α-keto acid or ammonia production, or using artificial dyes as final indicator of the flavin redox reaction.