Fungal pyranose oxidases: occurrence, properties and biotechnical applications in carbohydrate chemistry

Pyranose oxidases are widespread among lignin-degrading white rot fungi and are localized in the hyphal periplasmic space. They are relatively large flavoproteins which oxidize a number of common monosaccharides on carbon-2 in the presence of oxygen to yield the corresponding 2-keto sugars and hydrogen peroxide. The preferred substrate of pyranose oxidases is D-glucose which is converted to 2-keto-D-glucose. While hydrogen peroxide is a cosubstrate in ligninolytic reactions, 2-keto-D-glucose is the key intermediate of a secondary metabolic pathway leading to the antibiotic cortalcerone. The finding that 2-keto-D-glucose can serve as an intermediate in an industrial process for the conversion of D-glucose into D-fructose has stimulated research on the use of pyranose oxidases in biotechnical applications. Unique catalytic potentials of pyranose oxidases have been discovered which make these enzymes efficient tools in carbohydrate chemistry. Converting common sugars and sugar derivatives with pyranose oxidases provides a pool of sugar-derived intermediates for the synthesis of a variety of rare sugars, fine chemicals and drugs.