Different lethal effects by enzyme-generated triplet indole-3-aldehyde in different Escherichia coli strains.

Strains of Escherichia coli which lack 4-thiouridine (S4U) exhibit a higher survival rate than their wild-type parents which contain S4U after treatment with enzyme-generated triplet indole-3-aldehyde. In a similar manner to results obtained with monochromatic 334 nm UV light, the survival is related to single-strand breakage of DNA in E. coli containing the pBR 322 plasmid. The effects of the excited states generated by an enzymatic system suggest that S4U is an important chromophore in the lethal effects observed. The results also suggest that the energy transferred from triplet indole-3-aldehyde to S4U may also be passed from S4U of t-RNA to DNA, possibly through a singlet oxygen intermediate generated by excited S4U, resulting in a decrease in the survival rate of E. coli containing S4U. These results emphasize the importance of excited states in biological systems.