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J Bacteriol. 1972 October; 112(1): 653-655
Copyright © 1972 American Society for Microbiology. All Rights Reserved.

Toxicity of L-Tryptophan Photoproduct on Recombinationless (rec) Mutants of Salmonella typhimurium

^a Division of Biology, Kansas State University, Manhattan, Kansas 66502

ABSTRACT

L-Tryptophan after exposure to black light becomes toxic for recombinationless (rec) mutants of Salmonella typhimurium. Fifty-six radiation-sensitive mutants were screened for sensitivity to the tryptophan photoproduct; the rec and exr (X-ray sensitive) mutants are sensitive, whereas the uvr, hcr, and wild-type strains are resistant. A number of catabolic products of tryptophan and compounds related to tryptophan were screened for toxicity to rec strain; these are nontoxic or far less toxic for rec strains than irradiated L-tryptophan. The toxic photoproduct is relatively stable to drying and basic hydrolysis at 90 C, indicating that it is a stable organic compound, eliminating peroxide as the toxic component. It was also observed that the toxic product is a photooxidation product since it is formed only when L-tryptophan is irradiated in the presence of air.

¹ Present address: Division of Biological Sciences, University of Missouri-Columbia, Columbia, Mo. 65201.