A putative mechanism for H 2 O 2 production is shown in Fig. . After the primary reduction of Cu(II), O 2 binds to Cu(I), leading to the formation of a superoxide (O • - 2 ) species bound to Cu(II). From here, the reaction could proceed in two ways: (i) O • - 2 could be released from the active-site and form H 2 O 2 in solution, or (ii) LPMOs could form H 2 O 2 directly at their active-site through successive reduction and protonation (cf. Fig. ). However, the order of reduction and protonation is unknown. At several points during this reduction/protonation one could envisage release of a reactive oxygen species into solution that could lead to H 2 O 2 formation (shown in light blue in Fig. ).