Photodynamic action of proflavine on coliphage T3. I. Kinetics of inactivation.

The photodynamic inactivation of coliphage T3 was studied over a wide range of concentrations of the dye proflavine. With 2 x 10(7) phage/ml, two modes of inactivation were observed. Between 0.25 and 12 to 13 mug/ml, inactivation was biphasic. There was an initial first-order inactivation (Rx1) which became temporally associated with an apparently multiorder process (Rx2) at higher light doses. Dye concentrations above 12 to 13 mug/ml showed only two-target inactivation curves (Rx3), except at high dye concentrations where processes kinetically identical to Rx1 and Rx2 reappeared. Rx2 showed a normal rectangular hyperbolic saturation curve but Rx1 and Rx3 appeared to saturate prematurely. The saturation behavior of Rx1 and Rx2 was independent of phage concentration, but Rx3 was lost at phage titers above 2 x 10(7)/ml. No dark inactivation was seen with Rx1 and Rx2 subsequent to a period of illumination. With Rx3, an exponential dark inactivation was seen for at least 1 hr after a period of illumination. The dye-phage system equilibrated immediately, at any temperature, at proflavine concentrations where Rx1 and Rx2 occurred. With Rx3, prolonged equilibration times were necessary. Moreover, there was a temperature effect. The rate of inactivation at equilibrium was temperature-dependent, whereas the initial rate at which equilibrium was approached was essentially temperature-independent.