The tyrosine residue has long mystified LPMO researchers: it is widely conserved in most LPMO families, except for the majority of AA10 LPMOs, where it is replaced by phenylalanine. It seems now that it's role is to initialize a hole-hopping mechanism, known from other oxoreductase enzymes: a radical species ("hole") is generated close to the active site by a highly oxidizing species; this hole is then directed away (towards the surface) through electron-transfer chains comprised of aromatic/redox-active amino acids. Yet, detailed investigations of these reactions have been rare for oxoreductases; 44,45 and has only recently begun to appear for LPMOs. To confuse matter more, a hitherto undetected histidyl species was recently claimed to be observed through transient spectroscopy in LsAA9. The histidyl radical was assigned based on UV-vis absorption at 360 nm and high-energy-resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS).