Structures of diphthamide and B12 precursors and derivatives. (A) The core diphthamide pathway is predicted to contain three enzymes Dph2, Dph5 and Dph6 in Archaea. The formation of diphthine has been reconstituted in vitro using Dph2 and Dph5 from Pyrococcus horikoshii [4, 5]. The enzyme family catalyzing the last step in Archaea and Eukarya Dph6 was missing. In yeast, the first and last steps require additional proteins (Dph1, Dph3 and Dph7). (B) Predicted Dph6-catalyzed reactions. (C) Ado-Pseudo-B12 structure and hydrolysis site by the bacterial CbiZ enzyme (bCbiZ). Parts (A) and (B) are adapted with permission from Xuling Zhu; Jungwoo Kim; Xiaoyang Su; Hening Lin; Biochemistry 2010, 49, 9649–9657. Copyright 2010 American Chemical Society.