Photochemistry and Photobiology

Abstract— The photoreactivation of TMV–RNA‡ irradiated with either 253–7 mμ or 302 mμ light can be prevented by reconstitution of the virus from TMV–protein and the ultraviolet irradiated RNA. The prevention of photoreactivation by reconstitution is not irreversible as the RNA can be extracted from the reconstituted virus and is still capable of undergoing photoreactivation.

Abstract— Inactivation of tobacco mosaic virus RNA (TMV‐RNA) by u.v. radiation is slower in D₂O than in H₂O, and TMV‐RNA which has been inactivated in D₂O is photoreactivated faster (on Pinto bean) than TMV‐RNA which has been inactivated in H₂O. The maximum amount of photoreactivation is unaffected by the solvent, H₂O or D₂O, present during irradiation. These deuterium isotope effects for inactivation and photoreactivation suggest that pyrimidine hydrates are photoreactivable lesions on Pinto bean.

Abstract. The plaque forming ability of the E. coli phage fr, containing single stranded RNA, is highly UV‐resistant. One lethal hit corresponds to approximately 1'2 × 10⁵ erg cm^‐2. photoreactivation of fr due to illumination of infected bacteria has not been found after UV‐inactivation of either extracellular or intracellular phage. This shows that the already known PR‐enzyme of E. coli K12 is probably specific only for some of the UV‐lesions in DNA but not in RNA. Furthermore, it may indicate that the photoreactivation of some RNA‐containing plant viruse^(1,2) is due to a PR‐enzyme which is not present in K12.

UV‐inactivated fr is also not host‐cell‐reactivable. The plaque forming ability of fr infected bacteria decreases rapidly with increasing doses of PR‐light wherea: the colony forming ability of uninfected host cells is very resistant to PR‐light.

Abstract— Quantum yields for inactivation of infectivity of potato virus X by monochromatic ultraviolet radiation of wavelengths ranging from 230 to 290 nm, were measured with reference to energy absorbed by (a) the whole virus and (b) the virus RNA. The yields depended on the wavelength, but those with reference to energy absorbed by the RNA varied much less (with extreme values of 10^‐3 and 1.9 ± 10^‐3 than those with reference to whole virus. Consequently the action spectrum for inactivation of a dilute solution of the virus resembled the shape of the absorption spectrum of the RNA, but not closely enough to allow coincidence by adjusting the scales. The amount of photoreactivation increased as the wavelength increased and also as the year progressed from May to July; the extreme values of the photoreactivable sector were 0.43 and 0.86.

Abstract— Clover yellow mosaic virus, in common with other plant viruses with flexuous, rod‐like particles, can be photoreactivated. At lower U.V. doses, photoreactivation is masked by an inhibitory effect on virus infection of visible light alone.

Abstract— The formation of pyrimidine dimers on ultraviolet irradiation of TMV‐RNA in water is demonstrated in the region from 254 nm to 302 nm. No dimer is present in either unirradiated E. coli ribosomal RNA or TMV‐RNA. Dimer formation was also examined in TMV‐RNA irradiated in the presence of 5times10^‐6 M proflavin, in high salt, on dry ice, and in 90% methanol. No correlation of pyrimidine dimers with any biologically defined lesion is presently possible and it is suggested that dimer may not be involved in the inactivation of this material.

Abstract— A train of tobacco necrosis virus (TNV) and infective nucleic acid isolated from it (TNV‐RNA) are equally susceptible to inactivation by U.V. radiation at all wave‐lengths tested (230‐290 m_μ) and can be photoreactivated to the same extent by exposing inoculated host plants to daylight. The shape of the action spectrum for inactivation by U.V. of TNV and of TNV‐RNA follows that of the absorption spectrum of TNV‐RNA. Thus, unlike the RNA of tobacco mosaic virus, the RNA of TNV behaves in all these respects in the same way irrespective of whether it is inside or outside the virus particle. To inactivate TNV or TNV‐RNA to 50 per cent of their original infectivities, each mg of RNA must absorb about 0.27 joules of radiation energy of any wave‐length between 230 and 290 mp, which corresponds to a quantum yield of about 0.65 ×10^‐3 at 260 mμ.

A major difficulty in photodynamic therapy is the poor solubility of the photosensitizer (PS) under physiological conditions which correlates with low bioavailability. PS aggregation leads to a decrease in the photodynamic efficiency and a more limited activity in vitro and in vivo. To improve the aqueous solubility and reduce the aggregation of 2,9(10),16(17),23(24)‐tetrakis[(2‐dimethylamino)ethylsulfanyl]phthal‐ocyaninatozinc(II) (Pc9), the encapsulation into four poloxamine polymeric micelles (T304, T904, T1107 and T1307) displaying a broad spectrum of molecular weight and hydrophilic–lipophilic balance was investigated. The aqueous solubility of Pc9 was increased up to 30 times. Morphological evaluation showed the formation of Pc9‐loaded spherical micelles in the nanosize range. UV/Vis and fluorescence studies indicated that Pc9 is less aggregated upon encapsulation in comparison with Pc9 in water–DMSO 2% and remained photostable. Pc9‐loaded micelles generated singlet molecular oxygen in high yields. Photocytotoxicity assays using human nasopharynx KB carcinoma cells confirmed that the encapsulation of Pc9 in T1107 and T1307 increases its photocytotoxicity by 10 times in comparison with the free form in water–DMSO. In addition, Pc9 incorporated into cells was mainly localized in lysosomes.

Three potential photosensitizers for photodynamic therapy: tetra‐t‐butyl phthalocyaninato Zn(II), tetrakis‐(1,1‐dimethyl‐2‐phthalimido)ethylphthalocyaninato Zn(II), and tetrakis‐(1,1‐dimethyl‐2‐amino)ethylphthalocyaninato Zn(II), have been studied in homogeneous organic media. Dimerization constants and monomer and dimer spectra have been determined. Fluorescence, triplet and singlet oxygen quantum yìelds were measured and the photo‐physical characterization of the triplet state was performed for the three dyes. These parameters were evaluated in connection with aggregation results.