Lethal and mutagenic effect of the XeCl laser on Escherichia coli

The survival rate and reversions to tryptophan-independence of Escherichia coli after XeCl laser irradiation (lambda = 308 nm) within the dose range from 10(3) to 10(5) J/m2 have been studied to show that LD37 is 10(4) J/m2, the survival rate at a maximum dose of 10(5)J/m2 is 1 per cent, and the number of mutants per 10(6) cells survived is 100.     

Aggregation of crystallins induced by pulsed laser UV light (308 nm)

Here we compile and analyze the data on photoaggregation of a model protein carboanhydrase and the main eye lens proteins α-, β-, γ-crystallins under the action of pulsed UV irradiation from a Xe-Cl laser (308 nm) with broad variation of pulse energy density and repetition rate. The aggregation efficacy proves to be a nonlinear function of these parameters and protein concentration. A theoretical model is proposed that qualitatively explains the experimental data. It is shown that N-arm-truncated βA3-crystallin is more prone to UV-induced aggregation than the full-sized protein; such defects caused by mutation or aging may aggravate the development of lenticular opacity. Analyzed is the effect of some low-molecular compounds on the aggregation of β-crystallin and its mixture with α-crystallin. A combination of short peptides prepared on this basis markedly impedes crystallin aggregation and retards the development of UV-induced cataract in rats.     

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.     

Transmission of 308 nm excimer laser radiation for ophthalmic microsurgery--medical, technical and safety aspects

A surgical system using 308 nm excimer laser radiation transmitted by quartz fibers is described. In-vitro surgery has been performed on the cornea, in the anterior chamber angle, on the lens and in the vitreous with a special application tip for each procedure. Possible damage of ocular structures by 308 nm radiation is discussed. In-vitro experiments showed that UV exposure of intraocular structures sensitive to 308 nm radiation can be reduced by appropriate design of the application tips and by the application of UV absorbing drugs.     

Investigation of the mechanisms of crystallin aggregation induced by pulsed laser UV irradiation at 308 nm

The results of the investigations of photoaggregation of the main eye lens proteins alpha-, beta- and gamma-crystallins and the model protein carbonic anhydrase in response to pulsed irradiation by a XeCI laser at 308 nm in the wide range of pulse energy densities (w) and pulse repetition rates (F) have been reviewed. A nonlinear dependence of aggregation efficiency on the values of w, F, and the concentration of protein solution was found. A theoretical model that qualitatively describes the experimental results was developed. The aggregation of N-amino-arm truncated beta A3-crystallin was analyzed. It was found that the loss of the N-amino-arm as a result of mutation or eye lens aging increases the probability of UV-induced beta-crystallin aggregation, thereby increasing the predisposition of eye lens to senile cataract. The influence of some short-chain peptides on the aggregation efficiency of beta-crystallin and beta-crystallin in solution with alpha-crystallin was investigated. Based on the results obtained, a combination of peptides (called "a new preparation") was found that most effectively delays the crystallin aggregation. The preparation has been probed on experimental animals. The trials showed that the preparation increases the delay in the development of UV-induced cataract in rats. The possibility of designing a drug for the prophylaxis of the development of cataract in humans based on this preparation is discussed.     

Mutagenic interaction between near-(365 nm) and far-(254 nm)ultraviolet radiation in repair-proficient and excision-deficient strains of Escherichia coli.

The mutational interaction between radiation at 365 and 254 nm was studied in various strains of E. coli by a mutant assay based on reversion to amino-acid independence in full nutrient conditions. In the two repair-proficient strains (K12 AB 1157 and B/r), pre-treatment with radiation at 365 nm strongly suppressed the induction of mutations by far-UV, a phenomenon accompanied by a strong lethal interaction. The frequency of mutations induced by far-UV progressively declined with increasing dose of near-UV. Far-UV-induced mutagenesis to T5 resistance was almost unaltered by pre-treatment with near-UV. In AB 1886 uvrA there was no lethal interaction between the two wavelengths but the mutagenic interaction was synergistic. This synergism was maximal at a 365-nm dose of 8 X 10(5) J m-2. It is proposed that in the wild-type strain, cells containing potentially mutagenic lesions are selectively eliminated from the population because of abortive excision of an error-prone repair-inducing signal. In excisionless strains, 365-nm radiation may be less damaging to the error-prone than to the error-free post-replication repair system. Alternatively, mutation may be enhanced because of the occurrence of error-prone repair of 365-nm lesions by a system that is not induced in the absence of 254-nm radiation.