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

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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.

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