Catalyzes the oxidation of a range of monosaccharides in vitro, displaying the highest activity with N-acetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc), with a reduction of O2 to H2O2. Acts upon the C1 carbon of the GlcNAc or GalNAc molecule, producing the corresponding lactone, which can spontaneously hydrolyze. Its biological function is unclear, but its main function might be connected to extracellular production of hydrogen peroxide to compete with other organisms through oxidative stress, or support the action of peroxidases and peroxygenases. H2O + N-acetyl-D-glucosamine + O2 = H(+) + H2O2 + N-acetyl-D-glucosaminate H2O + N-acetyl-D-galactosamine + O2 = H(+) + H2O2 + N-acetyl-D-galactosaminate N-acetyl-D-glucosamine + O2 = H2O2 + N-acetyl-D-glucosamino-1,5-lactone N-acetyl-D-galactosamine + O2 = H2O2 + N-acetyl-D-galactosamino-1,5-lactone Binds 1 FAD per subunit in a bicovalent manner. kcat is 5.67 sec(-1) with N-acetyl-D-glucosamine as substrate. kcat is 4.46 sec(-1) with N-acetyl-D-glucosamine as substrate. kcat is 2.23 sec(-1) with N-acetyl-D-mannosamine as substrate. kcat is 0.84 sec(-1) with diacetylchitobiose as substrate. kcat is 0.35 sec(-1) with D-glucosamine as substrate. kcat is 0.62 sec(-1) with D-galactosamine as substrate. kcat is 0.011 sec(-1) with D-mannosamine as substrate. kcat is 0.16 sec(-1) with D-glucose as substrate. kcat is 0.19 sec(-1) with D-galactose as substrate. kcat is 0.14 sec(-1) with D-mannose as substrate. Optimum pH is 7.5. Belongs to the oxygen-dependent FAD-linked oxidoreductase family.