Reactivity of O 2 versus H 2 O 2 with polysaccharide monooxygenases

Significance Since the discovery of polysaccharide monooxygenases (PMOs), attention has focused on structure, function, and mechanism. The PMO copper active site can utilize oxygen or hydrogen peroxide to catalyze substrate oxidation. Although oxygen has been considered to be the physiologically relevant cosubstrate in the reaction, recent reports have focused on hydrogen peroxide. While oxygen is acknowledged as the cosubstrate utilized for other biological copper-dependent hydroxylations, there is no reason to rule out hydrogen peroxide for PMOs. This paper provides a detailed kinetic analysis and characterization of PMO reactivity with each cosubstrate. PMOs are capable of using either cosubstrate to oxidize the glycosidic linkage of cellulosic substrates, but different molecular mechanisms are accessed that affect enzyme activity and the products formed.