Detection of Antimetabolite Activity: Effects and Transport of Tryptophan Analogs in Escherichia coli

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Abstract
Simple and rapid techniques were developed that allow detection of the effects of a wide range of tryptophan analogs in Escherichia coli . (i) By using certain supersensitive mutant strains, analogs that were without effect on a wild-type strain were shown to be inhibitory. (ii) Many other analogs could inhibit the utilization of d -tryptophan when present as l -tryptophan replacements in a trp dadR strain. (iii) Another approach was to test the ability of a given analog to reverse the inhibition caused by an inhibitory analog. These combined approaches revealed activities in 26 analogs out of a total of 40 that were inactive by testing solely on a wild-type strain. The route of entry of inhibitory analogs was determined unambiguously by comparing their effect on aroP + (aromatic permease) and aroP strains. Uptake studies were also performed to determine whether various analogs compete for entry via the aromatic permease system. Many tryptophan analogs enter the cell via this system. The methods developed here should have general applicability to the testing of analogs of a variety of other metabolites.