Chorismase synthase, the enzyme catalyzing the final step of the shikimate pathway.
Chorismate synthase (CS; 5-enolpyruvylshikimate-3-phosphate phospholyase; 1-carboxyvinyl-3-phosphoshikimate phosphate-lyase; E.C. 22.214.171.124) catalyzes the seventh and final step in the shikimate pathway: the conversion of 5- enolpyruvylshikimate-3-phosphate (EPSP) to chorismate, a precursor for the biosynthesis of aromatic compounds. This process has an absolute requirement for reduced FMN as a co-factor which is thought to facilitate cleavage of C-O bonds by transiently donating an electron to the substrate, having no overall change its redox state. Depending on the capacity of these enzymes to regenerate the reduced form of FMN, chorismate synthases are divided into two classes: Enzymes, mostly from plants and eubacteria, that sequester CS from the cellular environment, are monofunctiona,l while those that can generate reduced FMN at the expense of NADPH, such as found in fungi and the ciliated protozoan Euglena gracilis, are bifunctional, having an additional NADPH:FMN oxidoreductase activity. Recently, bifunctionality of the Mycobacterium tuberculosis enzyme (MtCS) was determined by measurements of both chorismate synthase and NADH:FMN oxidoreductase activities. Since shikimate pathway enzymes are present in bacteria, fungi and apicomplexan parasites (such as Toxoplasma gondii, Plasmodium falciparum, and Cryptosporidium parvum) but absent in mammals, they are potentially attractive targets for the development of new therapy against infectious diseases such as tuberculosis (TB).