D-aspartate oxidase (DDO) is a flavoenzyme that selectively catalyzes the oxidative deamination of acidic D-amino acids, particularly D-aspartate and D-glutamate 1. DDO functions primarily in the cytosol and peroxisomal matrix, suppressing D-aspartate levels in the brain by degrading this amino acid that can act as a glutamate receptor agonist 1. This enzymatic activity protects organisms from D-amino acid toxicity and regulates intracellular levels of acidic D-amino acids derived from dietary and bacterial sources 1. DDO exhibits perfect enantioselectivity and stereoselectivity, making it valuable for biotechnological applications in identifying and quantifying acidic D-amino acids 1. Clinically, genetic variants in DDO have been associated with non-small cell lung cancer survival outcomes; a DDO SNP (rs9384742) correlated with decreased mRNA expression and reduced expression in lung cancer tissue, influencing patient overall survival 2. The enzyme participates in peroxisomal metabolic pathways that regulate reactive oxygen species, linking DDO function to cellular redox homeostasis and potentially cancer progression 2.