Notably, the larger distance in TaAA9 means that we can optimize a stable intermediate after breaking of the hydrogen bond to Gln, but this intermediate is close to degenerate with TS I , and we have therefore not included it in Fig. (a full Figure including this intermediate is given in the SI, see Fig. and). Interestingly, the hydrogen bond to Gln is re-formed in 2 (with a distance of 1.7 Å in TaAA9 and 1.8 Å in LsAA9), where the OH group is now coordinated to Cu(II). Other distances are roughly similar (cf. Table ), so the energetic differences between the reaction barrier of the two LPMOs in Fig. may be traced back to the structural differences in the local hydrogen bonding of Gln to the transition state.