Catalyzes the FAD-dependent oxidative deamination of various amines and D-amino acids to yield the corresponding alpha-keto acids, ammonia/amine, and hydrogen peroxide. Oxidizes glycine, sarcosine (N-methylglycine), N-ethylglycine, D-proline, D-alanine, glycine-ethyl ester, and some other D-amino acids. Does not act on L-proline (PubMed:17894345). Is essential for thiamine biosynthesis since the oxidation of glycine catalyzed by ThiO generates the glycine imine intermediate (dehydroglycine) required for the biosynthesis of the thiazole ring of thiamine pyrophosphate (By similarity). glycine + H2O + O2 = glyoxylate + H2O2 + NH4(+) H2O + N-ethylglycine + O2 = ethylamine + glyoxylate + H2O2 H2O + O2 + sarcosine = glyoxylate + H2O2 + methylamine D-alanine + H2O + O2 = H2O2 + NH4(+) + pyruvate Binds 1 FAD per subunit. Is inhibited at high substrate concentration. Vmax with D-proline as substrate is 1.4-, 2.75-, 3.5- and 4.3-fold higher than with glycine, sarcosine, D-alanine, and N-ethylglycine, respectively. Optimum pH is 8.5. Is stable in the pH 6-9.5 range. A great decrease in stability is only produced at pH values below pH 4.0. Thermostable. Displays a Tm value of 2.5 hours at 60 degrees Celsius, and 0.6 hour at 80 degrees Celsius. Cofactor biosynthesis; thiamine diphosphate biosynthesis. Homotetramer. Belongs to the DAO family. ThiO subfamily.