We can also compare structures of 1 and 2 as well as the transition state in the two LP-MOs in Fig. . For both enzymes, the largest structural change between 1 and 2 is the change in the Cu-O Tyr bond, which shortens from 2.6 Å (both enzymes) in 1 to 2.4 Å (TaAA9) or 2.2 Å (LsAA9) in 2. Thus, the de-protonation of tyrosine leads to coordination of the tyrosyl, consistent with a previous calculation on LsAA9. In both enzymes, the tyrosine OH-group forms a hydrogen bond to a Gln residue in 1 (the bond-distance is 1.6 Å in both TaAA9 and LsAA9). This hydrogen bond is partly broken in the transition state; here TaAA9 and LsAA9 are different as the bond distance is 2.3 Å in TaAA9 and 2.1 Å in LsAA9.