Effect of Tryptophan Analogs on Derepression of the Escherichia coli Tryptophan Operon by Indole-3-Propionic Acid

Document Type




Format of Original

8 p.

Publication Date



American Society for Microbiology

Source Publication

Journal of Bacteriology

Source ISSN


Original Item ID

DOI: 10.1128/jb.136.1.219-226.1978


The abilities of 14 tryptophan analogs to repress the tryptophan (trp) operon have been studied in Escherichia coli cells derepressed by incubation with 0.25 mM indole-3-propionic acid (IPA). trp operon expression was monitored by measuring the specific activities of anthranilate synthase (EC and the tryptophan synthase (EC β subunit. Analogs characterized by modification or removal of the α-amino group or the α-carboxyl group did not repress the trp operon. The only analogs among this group that appeared to interact with the trp aporepressor were IPA, which derepressed the trp operon, and d-tryptophan. Analogs with modifications of the indole ring repressed the trp operon to various degrees. 7-Methyl-tryptophan inhibited anthranilate synthase activity and consequently derepressed the trp operon. Additionally, 7-methyltryptophan prevented IPA-mediated derepression but, unlike tryptophan, did so in a non-coordinate manner, with the later enzymes of the operon being relatively more repressed than the early enzymes. The effect of 7-methyltryptophan on IPA-mediated derepression was likely not due to the interaction of IPA with the allosteric site of anthranilate synthase, even though feedback-resistant mutants of anthranilate synthase were partially resistant to derepression by IPA. The effect of 7-methyltryptophan on derepression by IPA was probably due to the effect of the analog-aporepressor complex on trp operon expression.


Published version. Journal of Bacteriology, Vol. 136, No. 1 (October 1978): 219-226. DOI. © 1978 American Society for Microbiology. Used with permission.