[CuOH] + moiety coordinated to a tyrosyl radical. Tyrosyl radicals have now been observed for a number of LPMOs and are characterized by having UV-vis spectra with strong, sharp absorption features around 400-420 nm. We note in passing that one investigation 39 (for LsAA9) showed rather different features, and based on quantum-mechanics/molecular mechanics and time-dependent density functional theory (TD-DFT), we 40 have argued that this spectrum originated in a different species (trans-[TyrO • -CuOH] + in Fig. ).