Chorismate synthase catalyzes the 1,4-elimination of phosphate and the C-(6-pro-R) hydrogen from 5-enolpyruvylshikimate 3-phosphate (EPSP) to generate chorismate. Although this reaction does not involve an overall change in redox state, the enzyme requires reduced FMN. To investigate the role of the flavin in catalysis we have employed chemically modified flavins: 1- and 5-deaza-, 2- and 4-thio...