Catalyzes the oxidation of various aldopyranoses and disaccharides on carbon-2 to the corresponding 2-keto sugars concomitant with the reduction of O(2) to H(2)O(2). Plays an important role in lignin degradation of wood rot fungi by supplying the essential cosubstrate H(2)O(2) for the ligninolytic peroxidases, lignin peroxidase and manganese-dependent peroxidase. The preferred substrate is D-glucose which is converted to 2-dehydro-D-glucose, an intermediate of a secondary metabolic pathway leading to the antibiotic cortalcerone. Acts also on D-xylose, together with D-glucose the major sugars derived from wood, on L-sorbose, D-galactose and 1,5-anhydroglucitol, a diagnostic marker of diabetes mellitus. D-glucose + O2 = 2-dehydro-D-glucose + H2O2 Binds 1 FAD covalently per subunit. Optimum pH is 6. Active and stable from pH 3 to 9. Optimum temperature is 30-50 degrees Celsius. Active and thermostable for 30 minutes up to 55 degrees Celsius. Homotetramer. Hyphal periplasmic space. Belongs to the GMC oxidoreductase family.