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 (By similarity). D-glucose + O2 = 2-dehydro-D-glucose + H2O2 Binds 1 FAD covalently per subunit. Optimum pH is 5.5-6.5. Homotetramer. Hyphal periplasmic space. Belongs to the GMC oxidoreductase family.