PROFLAVINE MEDIATED PHOTOINACTIVATION OFBACTERIOPHAGE φX174 AND ITS ISOLATED DNA: EFFECTS OF AGENTS MODIFYING VARIOUS PHOTOCHEMICAL PATHWAYS

Abstract. Thiols and disulfides protect both φX174 phage and its isolated DNA from the lethal action of proflavine plus light. The protective ability of these compounds appears to be attributed to the -SH or the -S-S- group and the property to interact with the proflavine-phage DNA complex. The phage inactivation efficiency per proflavine bound to DNA is reduced by 50 to 30% upon addition of cysteine or cystamine. Substances that affect the lifetime of singlet oxygen modify the rate of phage photoinactivation in the presence of proflavine; the inactivation rate is decreased by N^-₃ and increased by D₂O. Irradiation under N₂ atmosphere markedly decreases the phage photosensitization by proflavine. Irradiation with monochromatic light of 440 nm is less efficient than irradiation with light of 440 nm plus 360 nm, and the difference is more pronounced in N₂ than in air. These results are discussed in relation to various possible photochemical pathways.     

INDUCTION OF FREE RADICALS IN DNA BY PROFLAVINE AND VISIBLE LIGHT: INFLUENCE OF OXYGEN AND IONIC STRENGTH

Abstract —The photosensitization of native DNA is observed as an induction of free radicals in the DNA moiety of proflavine-DNA complexes. The intensity of the electron paramagnetic resonance spectra (at 77 K) is a measure of the number of free radicals present in frozen solutions of DNA-proflavine complexes after irradiation with visible light (Λ > 320 nm). In the absence of O₂, the photosensitization is significant but very low; it increases slightly with increasing NaCl ionic strength; it appears to be due to intercalated dye molecules and the qualitative analysis of the spectra obtained shows that mainly thymidine is involved. The reaction measured after saturation with O₂ is the same as the reaction in air but is quantitatively higher; the free radicals observed are peroxides. This induction of free radicals appears to be due to the intercalated dye molecules, each molecule acting independently. The important observation is a very sharp and large (around a hundred-fold) increase in the photosensitizing efficiency of the bound dye molecules occurring in NaCl between μ, # 0–25 and μ= 0–5 and in MgCl₂ between μ# 0–01 and μ=0–1.     

PROFLAVINE PHOTOSENSITIZATION OF DOUBLE AND SINGLE STRANDED DNA: EPR STUDY OF THE EFFECT OF VARIOUS SULPHUR-CONTAINING SUBSTANCES

Abstract—The proflavine-mediated photosensitization of both double-stranded calf thymus and single-stranded DNA from bacteriophage φ× 174 was followed in terms of the induction of free radicals in frozen solutions by EPR measurements in the presence of oxygen. The effect of the addition of various sulphur-containing substances to the proflavine DNA mixtures was studied and quantitatively expressed for definite amounts of proflavine bound to both DNAs.
Upon irradiation with visible light, RS radicals were observed in the presence of these sulphur-containing substances. Some of them caused a decrease in the amount of peroxide radicals normally induced in the photosensitized DNA. This decrease appeared to be linked to the property of the compounds to interact with DNA in such a way that they modify the binding of proflavine to DNA.
Cysteine, cysteamine, cystamine and cystine, protect calf thymus DNA against the "proflavine and light" free radical induction by 55, 58, 64 ahd 62% respectively. φ× 174 single-stranded DNA is also protected by the addition of cysteamine and cystamine, although to a lesser extent than calf thymus DNA (35%). These protection factors were measured under conditions where strong binding of the dye to the DNA was predominant.