The peroxygenase reaction circumvents the requirement for external protons and electrons (see reactions 5b-7b in Figure ), and for the LPMOs where mono-and peroxygenase reactions have been compared, the latter is orders of magnitude faster. For a few cases, the catalytic reaction has also been performed anaerobically, showing that these LPMOs indeed exclusively use H2O2 (according to Scheme 2 or reactions 5b-7b in Figure ). However, whether this is true for all LPMOs is still controversial. Moreover, it is also unknown if some LPMOs can use H2O2 as a "peroxide shunt" pathway as some iron-heme enzymes (see further below). A complicating factor for experimental investigations concerning the co-substrate is that LPMOs can catalyse the offpath oxidase reaction