Fig. 6.

Reaction mechanism of the AmiD amidase proposed by Kerff et al. (124). The scheme describes the catalytic mechanism for the AmiD hydrolysis of the MurNAc-l-Ala amide bond. (A) Activation of the catalytic water molecule by Zn²⁺ and Glu104 upon binding of the substrate; (B) formation of the tetrahedral intermediate stabilized by Zn²⁺ and Lys159; (C) rotation of the amide bond leading to an ideal tetrahedral conformation of the amide bond nitrogen; (D) transfer of the hydrogen from the protonated Glu104 to the amide nitrogen and cleavage of the amide bond. R, remaining peptide moiety.