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). D-glucose + O2 = 2-dehydro-D-glucose + H2O2 Binds 1 FAD covalently per subunit. Homotetramer. Belongs to the GMC oxidoreductase family.