Abstract
Abstract— Urocanic acid (UA) has previously been shown to react photochemically in vitro with N,N‐dimethylthymine. In this study, mixtures of UA and phage G4 single‐stranded DNA have been irradiated with UV light (λ≥ 254 nm) and the DNA assayed for infectivity. At the concentrations of UA employed (typically 5.4 × 10‐3M) there is extensive absorption of the incident light by the UA. The DNA is inactivated at rates greater than that predicted from the calculated shielding by UA, indicating that photosensitization is occurring. Photosensitization is also indicated by the fact that at high UA concentrations the inactivation rate does not decrease to zero but approaches a residual value. Furthermore, the ability to photoreactivate DNA that has been photolyzed in the presence of UA is much reduced relative to that observed upon photolysis of the DNA alone. UA is therefore responsible for the production of UV‐induced DNA lesions, which are resistant to photoreactivation.A general analysis of the effects of photosensitization on the kinetics of UV inactivation is presented in an appendix.
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