Catalyzes the oxidation of glycine, leading to glyoxyl imine and hydrogen peroxide as primary products; glyoxyl imine is used for the biosynthesis of the thiazole ring of thiamine. Otherwise, glyoxyl imine is spontaneously hydrolyzed in water to produce glyoxylate and ammonia. Can also use sarcosine (N-methylglycine) as substrate, and, to a lesser extent, N-ethylglycine and D-proline. Has no activity towards other amino-acids D-Asp, D-Glu, D-Gln, D-His, D-Leu, D-Lys, D-ornithine, D-Trp, D-Val, L-Ala, L-Asp, L-Glu, L-His, L-Leu, L-Lys, L-Met and L-Pro. glycine + H2O + O2 = glyoxylate + H2O2 + NH4(+) H2O + O2 + sarcosine = glyoxylate + H2O2 + methylamine Optimum pH is 8.5. Optimum temperature is 40 degrees Celsius. Cofactor biosynthesis; thiamine diphosphate biosynthesis. Monomer. Belongs to the DAO family. ThiO subfamily.