LmU and GlmV reactions are carried out by a single bifunctional enzyme called GlmU. The GlmV enzyme of C. trachomatis is not homologous with the Cterminal portion of E. coli GlmU. GlmV exemplifies a case where a high-Trp analog has evolved as a functional replacement of a lowTrp analog. A number of such up-Trp (or down-Trp) replacements are enumerated in this article. The extent to which the GlmV