PHOTODYNAMIC EFFECTS OF PROFLAVINE ON BACTERIOPHAGE φ times 174 AND ITS ISOLATED DNA

Proflavine‐mediated photoinactivation of φ times 174 phage and its isolated DNA was studied under identical irradiation conditions. The inactivations followed single‐hit kinetics and a linear relationship was obtained in reciprocal plots of the inactivation rates vs the proflavine concentrations for both phage and isolated DNA. The phage photoinactivation rate was increased with an increase in the amount of proflavine bound to the phage DNA in a strong binding range (0.01‐0.04 proflavine/ nucleotide) as the total proflavine concentration was increased or the ionic strength decreased. Further, a phage‐specific factor was also found to affect the inactivation rate. The photodynamic treatment induced mutations in three phage strains from “amber” to “wild type” at a mutation rate per lethal hit of 0.3 times 10 ‐5 to 2.6 times 10 ‐5 . In contrast to phage infectivity, the φ times 174 DNA infectivity was measurable only at a high multiplicity of infection, and its photoinactivation occurred only at high proflavine concentrations. The photoinactivation rate was enhanced either with a decrease in the multiplicity of infection or with the use of spheroplasts of recA mutants strains. The results are discussed in terms of the nature of and possible repair mechanisms of photodynamically induced lesions in φ times 174 phage DNA.