Photoinactivation of cellular catalase by ultraviolet radiation

Summary

Photoinactivation of catalase is found to be similar in solution and in human normal skin fibroblasts exposed to ultraviolet B, ultraviolet A and near visible light, and the kinetics of such photoinactivation obey first order processes. The action spectrum, measured for the first time in cells, suggests that catalase photoinactivation in solution and in cells proceeds via similar routes. In both systems, no protective effect was observed with diethyldithiocarbamate, a superoxide dismutase inhibitor, with desferrioxamine, an iron chelator which impedes the production of hydroxyl radical via the Fenton reaction, and with vitamin E which scavenges peroxyl radical to protect against membrane peroxidative process. While the absence of protection by these inhibitors may be anticipated for the photoinactivation of catalase in solution, the lack of effect in cells suggests that reactive oxygen species produced by endogenous photosensitization are not responsible for the enzyme inactivation. Moreover, the already established protective effect of ethanol in solution is also observed in cells, supporting the view that photoinactivation in solution and in cells is due to the same primary events.     

Effects of peroxide and catalase on near ultraviolet radiation sensitivity in Escherichia coli strains

The role of peroxide and catalase on NUV radiation sensitivity was examined in two repair competent E. coli strains, AB1157 and B/r. Exponential phase B/r is considerably more sensitive to NUV radiation than exponential phase AB1157. However, resistance to 5 mmol dm-3 H2O2 was induced in both AB1157 and B/r by pretreating growing cells with 30 mumol dm-3 H2O2. Pretreatment also induced resistance to broad-band NUV radiation in these strains. The addition of catalase to the post-irradiation plating medium increased survival to the same extent as that provided by pretreatment with 30 mumol dm-3 H2O2, in both strains. The NUV radiation sensitivity seen in B/r does not appear to be due to a deficiency in enzymes that scavenge H2O2, as a catalase deficient mutant, E. coli UM1, is more resistant to NUV radiation than B/r. Also, assays for H2O2 scavenging ability show little difference between AB1157 and B/r in this respect. Two hypotheses are put forward to account for the sensitivity of exponential phase B/r. Whilst it is apparent that peroxides and catalase do have a role in NUV radiation damage, it is clear that other factors also influence survival under certain conditions.     

Combined action of ultrasound and ionizing radiation on yeast cells

Summary This communication reports the observation of synergistic relationships between ultrasound and gamma-irradiation of stationary phase cultures ofSaccharomyces cerevisiae of different strains. The gamma-ray dose was applied before or after the sound. The extent of synergism depended upon the sequence of application; it was smaller for (US +-ray)-exposure in comparison with (-ray + US)-treatment. The combined action of both modalities had smaller or no synergistic effect for mutant (rad51) yeast cells incapable of recovery. On this basis, it was concluded that possible mechanisms for ultrasound radiosensitization of yeast cells may involve the reduced capacity of cells to recover damages resulted from the combined action and/or the enhanced expression of lethal damage.     

Abiogenic synthesis of oligonucleotides on kaolinite under the action of ultraviolet radiation

Summary The present work deals with the processes involved in the abiogenic polycondensation of nucleotides adsorbed on the clay mineral kaolinite under the action of ultraviolet (UV) radiation. The dependence of the yield of synthesis products on irradiation dose was studied. The maximum yield corresponds to a 6-h exposure. The newly synthesized substances were analyzed by ion-exchange chromatography. Some fractions were studied for the type of bonds they contained by venom phosphodiesterase and RNase T₂ enzymatic hydrolysis. It was determined that some of the products synthesized by exposure of AMP adsorbed on the surface of clay particles to UV radiation may be looked upon as oligonucleotides in which some fragments have 2–5-bonded and others 3–5-bonded nucleotides     

Long time combined action of cadmium and ultraviolet radiation on barley plants

In a greenhouse experiment the development of biomass and grain yield was studied under a long-time combined action of medium-wave UV-radiation and cadmium (exposure levels of the agents were, respectively, 0.65-1.30 W/m2, 5 and 50 mg/kg of soil). The influence of the metal on the UV-radiation induced inhibition of the vegetative mass development was found to be dependent on the duration of stress: with increase in the exposure time the cadmium ability for cushioning negative effects of irradiation decreases. Simultaneously the contribution of the metal and its interaction with UV-radiation to the variability in the observed indicator (biomass) becomes much less significant than that of irradiation. Considerable independent of cadmium concentration reduction in the grain yield becomes evident at a rate of medium-wave UV-radiation intensity of 0.65 W/m2, whereas at UV-radiation exposure levels of 1.30 W/m2 and the heavy metal concentration of 50 mg/kg in soil practically total inhibition of grain productivity occurred. As for grain formation, relative effects of irradiation were somewhat higher than these of cadmium and its interaction with UV-radiation.     

The prognosis of the portion of irreversible radiation damages after simultaneous action of hyperthermia and ionizing radiation on yeast cells

The results of experimental research of diploid yeasts cells survival after simultaneous action of hyperthermia and ionizing radiation (60Co) have been described. It was shown that the cell ability to liquid holding recovery decreased with an increase in the temperature, at which the exposure was carried out. due to the increase in the irreversible component determining the relative part of radiation damage which cells are incapable to recover. To predict theoretically the relative part of irreversible radiation damage after combined action, the mathematical model was suggested taking into account the synergistic interaction of agents. Good correlation between experimental results and model prediction was demonstrated. The importance of the results obtained for the interpretation of the mechanism of synergistic interaction of various factors is discussed.     

The accelerating action of illumination in recovery of Arbacia eggs from exposure to ultraviolet radiation

Light of wave lengths 0.30µ to 0.50µ, accelerates return of the cleavage rate of Arbacia eggs to normal, after delay by exposure to ultraviolet radiation (wave lengths 0.238µ to 0.31µ). Recovery is apparently complete. Wave lengths 0.30µ to 0.50µ have no effect on the cleavage rate of normal eggs, nor does such illumination previous to dosage with ultraviolet radiation influence subsequent recovery. Acceleration of recovery of the egg occurs before fertilization as well as after. The effects of ultraviolet radiation and recovery therefrom are essentially the same in nucleated "white halves" as in the intact eggs. This phenomenon in the Arbacia egg seems basically comparable to photoreactivation of bacteria and fungi.     

The action of acriflavine on yeast protoplasts

Summary The effect of acriflavine on protoplasts of a strain ofSaccharomyces carlsbergensis has been compared with the effect on intact cells of the same strain. The strain was typical of the species in that little or no mutation occurred when young cells were exposed to acriflavine at concentrations up to 50 μg/ml for 4 hours. However, after exposure of protoplasts, prepared by the action of snail crop juice, to acriflavine at concentrations up to 10 μg/ml for the same period, the rate of oxidation of acetate was reduced by 45% whereas the rate of fermentation of glucose remained unchanged. It is concluded that the susceptibility of cells to acriflavine may be dependent on the resistance of cell wall material to penetration by the dye, thus controlling the rate of entry into the cytoplasm.     

Apoptosis induced by ultraviolet radiation is enhanced by amplitude modulated radiofrequency radiation in mutant yeast cells

The aim of this study was to investigate whether radiofrequency (RF) electromagnetic field (EMF) exposure affects cell death processes of yeast cells. Saccharomyces cerevisiae yeast cells of the strains KFy417 (wild-type) and KFy437 (cdc48-mutant) were exposed to 900 or 872 MHz RF fields, with or without exposure to ultraviolet (UV) radiation, and incubated simultaneously with elevated temperature (+37 degrees C) to induce apoptosis in the cdc48-mutated strain. The RF exposure was carried out in a special waveguide exposure chamber where the temperature of the cell cultures can be precisely controlled. Apoptosis was analyzed using the annexin V-FITC method utilizing flow cytometry. Amplitude modulated (217 pulses per second) RF exposure significantly enhanced UV induced apoptosis in cdc48-mutated cells, but no effect was observed in cells exposed to unmodulated fields at identical time-average specfic absorption rates (SAR, 0.4 or 3.0 W/kg). The findings suggest that amplitude modulated RF fields, together with known damaging agents, can affect the cell death process in mutated yeast cells. Bioelectromagnetics 25:127-133, 2004.