Tryptophan photoproduct(s): sensitized induction of strand breaks (or alkali-labile bonds) in bacterial deoxyribonucleic acid during near-ultraviolet irradiation.

Long-wavelength ultraviolet light (300 to 400 nm) converts L-tryptophan to a photoproduct that is toxic for bacterial cells in dark conditions. We now report that similar photoproducts of l-tryptophan sensitize bacterial deoxyribonucleic acid to 365-nm radiation, increasing the yield of deoxyribonucleic acid strand breaks (or alkali-labile bonds) by approximately 11.5-fold. Evidence is also presented which indicates that thse sensitized deoxyribonucleic acid lesions contribute to lethality for Escherichia coli irradiated with 365-nm ultraviolet light in suspensions of tryptophan photoproducts.