Биологические науки /9. Биохимия и биофизика

Candidate of Biology E. V. Pinyaskina

Establishment of the Russian Academy of Sciences Pricaspian institute

of Biological resources of the Dagestan centre of science of the RAS

Protective photoeffects induced by low-intensive red light

At present, the known types of photoinduced cell reactivation and defense [5,8] are aimed at the removal or prevention of one type of lethal photoproducts, namely, pyrimidine dimers, which are formed in DNA affected by far- and middle- wavelength ultraviolet (UV) radiation (220-320 nm). So far, no data is available on the photoinduced increase in viability of cells, inactivated by near-UV radiation (320-380 nm) and visible light (400-600 nm). Contrary to short wavelength UV radiation, the lethal effect of optical radiation of these types occurs via a photodynamic mechanism involving endogenous sensitizers, which generate reactive oxygen species that induce DNA damage other than that of pyrimidine dimers [1,6,7]

The purpose of this study was to reveal the effects of photorecovery in yeast cells during their photodynamic inactivation by optical radiation at wavelengths of 320380 nm and 400-600 nm.

Our studies of the effect of monochromatic light at 400-730 nm on C. guilliermondii cells, which were inactivated by near UV radiation (320-380 nm), have shown that the light of the red part of the spectrum (610, 630, 660, 680, 710 nm) significantly increases their viability. As has been established (data not shown), the maximal activity in the expression of yeast photoreactivity is exerted by light at 680 nm; we shall designate it further as FR680.

The typical curve characterizing the effect of red light (680 nm) on the photoreduction of cell viability is shown at Fig.1. The maximal level FR680 is reached already at short-term (several minutes) irradiation by monochromatic light at low dose. The increase in time radiation.

Fig. 1. The effect of monochromatic (680 nm) light irradiation dose at 22°C (1) and at 4°C (2) on photoreduction of C. guilliermondii cells inactivated by near UV (320-380 nm; 70 kJ/m²).

Viability, %

0 25 50 75

Dose, kJ m ²

Fig. 2. Viability curves for S. cerevisiae irradiated by near UV (320-380 nm): (1) wild type strain; (2) mutant strain rad 50-1.

It is necessary to mention that the established shape of the FR₆₈₀ dose curve mirrors the shape of corresponding curves that we obtained in our studies on the resuscitation induced by monochromatic red light in yeasts C. guilliermondii, previously inactivated by middle wavelength UV radiation (290-320 nm) [4]. In addition we have shown that the efficiency of FR₆₈₀ in the near UV for cell inactivation is not affected by the temperature decrease to 4°C during monochromatic irradiation (Fig. 1). The same was also observed previously in case of middle wavelength UV radiation [4].

These data suggest that in the photorecovery of cells from the lethal effect of near UV radiation, the same system is responsible - sensitive to red light and involved in the effect of middle wavelength radiation. This further indicates the efficiency of this system in respect to both pyrimidine dimers and photodynamic DNA damage, such as monostrand breaks, which under near UV radiation are important for cell inactivation [1,7].

It is well established that UV-induced damage can be repaired mainly by excision and post-replicative DNA reparation systems. Therefore it was worth to examine the possible association between FR₆₈₀ radiation and photoinduced activation of these reparation systems.

Dose, kJ m ²

Fig. 3. Viability curves for S. cerevisiae irradiated by middle wavelength UV (290-320 nm): (1) wild type strain; (2) mutant strain rad 3-2.

Viability, %

Dose, Jm ²

Fig. 4. The effect of monochromatic (680 nm) light irradiation dose on photoreduction of S. cerevisiae cells inactivated by near UV (320-380 nm): (1) wild type strain; (2) mutant strain rad 50-1. Doses of near UV irradiation: 70 (1) and 30 kJ/m² (2).

For this purpose we studied the capacity to FR₆₈₀ of yeasts C. cerevisiae, both wild type and its mutants deficient in excision (rad 3-2) and post-replicative (rad 50-1) DNA reparation. It has been shown previously that cells of a mutant strains are more sensitive to the near UV (rad 50-1) and middle wavelength UV (rad-3-2) compared to the wild type strain (Figs. 2, 3). The photo- reactivation experiments were conducted according to the following protocol. Both wild type and mutant, rad 50-1 and rad 3-2, cells were irradiated by fixed doses of near UV or middle wavelength UV, which decreased their viability to the same level (~30%). After that, they were irradiated by monochromatic light, 680 nm. The results (Se on Figs. 1,4) show that FR₆₈₀ in mutant strains was observed with the same efficiency as in wild type yeasts. This indicates the lack of excision or postreplicative reparation in the photorecovery of yeasts inactivated by UV radiation.

The fact that the effect of a light-sensitive reactive system is not specific to DNA damage leads to the suggestion that it is possibly involved in cell recovery from photodamage both in the genome and other cell structures.

Earlier, our studies have shown that under photodynamic inactivation of yeasts (C. guilliermondii and S. cerevisiae) by high doses of visible light (400-600 nm), cytoplasm, but not DNA, is the main target [6]. The results presented here, and which involve the above-described optimal doses at FR₆₈₀, have shown that a cell inactivated by visible light can be recovered by monochromatic irradiation in the wavelength range of 600-730 nm with the highest efficiency of reactivation at 680 nm. Most important is the fact that the typical curve of photoreactivation dose in this case has the same shape of curves as an analogous dose at FR₆₈₀ for cells inactivated by UV radiation (see Figs. 1,4). Therefore, the photoreduction of viability of yeast cells inactivated by visible light involves the same light-sensitive system as that activated with a lethal dose of UV radiation. Therefore, this inactivation system functions not only during the induction of various types of DNA damage, but also in case of photodynamic destruction of plasma membranes.

The similarity in photoreduction effects for yeast cell viability when they are inactivated both with UV irradiation and visible light indicates that they are based on an identical, previously unknown, photo-induced reactivating mechanism, which is not specific in respect to the nature of lethal damage.

REFERENCES

1. Burchuladze, T.G. and Fraikin, G.Ya., The Studies of the Mechanism of HADH-sensibilizing Formation of DNA Nicks at Irradiation by Near UV-light, Mol. Biol., 1991, vol. 25, no. 4, pp. 955-959.

2. Korogodin, V.I., Types of Yeast Cells Inactivation by Ionizing Radiation, Biophysics, 1958, vol. 3, no. 2, pp. 206209.

3. Strakhovskaya, M.G., Ivanova, E.V., and Fraikin, G.Ya., Stimulating Effect of Serotonin on the Growth of Yeasts Candida guilliermondii and Bacteria Streptococcus fac- calis, Microbiology, 1993, vol. 62, no. 1, pp. 46-49.

4. Fraikin, G.Ya., Pinyaskina, E.V., Strakhovskaya, M.G., Rubin, A.B., New Photoinduced Defence System in Candida guilliermondii Cells at Lethal Effect of Middle Wavelength Ultraviolet Radiation, Dokl. Akad. Nauk, 1995, vol. 343, no. 2, pp. 265-267.

5. Fraikin, G.Ya., Photoprotection by serotonin, in Biological Effect of Light, Berlin: New York, 1992, pp. 458-462.

6. Fraikin, G.Ya., Strakhovskaya, M.G., and Rubin, A.V., The Role of Membrane Bound Porphyrin-Type Compound as Endogenous Sensitizer in Photodynamic Damage to Yeast Plasma Membranes, J. Potochem. Potobiol. B Biol., 1996, vol. 34, no. 1, pp. 129-135.

7. Peak, J.G., Peak, M.J., and MacCoss, M., DNA Breakage Caused by 334 nm UV-light is Enhanced by Naturally Occurring Nucleic Acid Components and Nucleotide Coenzymes, Photochem. Photobiol., 1984, vol. 39, no. 6, pp. 713-716.

8. Sancar, G.B., DNA Photolyases: Physical Properties, Action Mechanism and Roles in Dark Repair, Mutat. Res., 1990, vol. 236, pp. 147-160.