E. Riklis

Bio: E. Riklis is an academic researcher from Israel Atomic Energy Commission. The author has contributed to research in topics: DNA repair & Nucleotide excision repair. The author has an hindex of 7, co-authored 11 publications receiving 177 citations.

Photochemical reactions of chlorpromazine; chemical and biochemical implications.

Abstract: — The photoexcited chlorpromazine reacts with methanol to yield promazine and 2-methoxypromazine by two different reaction pathways: hydrogen atom abstraction and nucleophilic attack. respectively. When the photoexcitation of chlorpromazine is performed in the presence of protein or nucleic acids, chlorpromazine binds to the biopolymer. This binding is drastically pH-dependent and correlates to the phototoxic effect exhibited in chlorpromazine—photosensitization of E. coli. No photodynamic damage of E. coli attributed to CPZ-sensitization of molecular oxygen could be detected.

Enhancement of thermal killing by polyamines. I. Survival of Chinese hamster cells.

Abstract: Exposure of Chinese hamster cells to polyamines at an elevated temperature (42 degrees C) results in synergistic cell killing. The effectiveness of polyamines in potentiating thermal killing decreases in the following order: spermine greater than spermidine greater than cadaverine greater than putrescine. The magnitude of the synergism increases with exposure time. The survival curves, when plotted as a function of polyamine concentration, display a shoulder during 1 h exposure at 42 degrees C, followed by exponential cell killing. Longer exposure times eliminate the shoulder and result in steeper slopes of the survival curves. The effect is maximal when exposure to polyamines and heat is simultaneous. Separation in time between the two treatments causes a rapid disappearance of the synergism. The order of application is of only minor importance in this regard. The results suggest that the intracellular level of spermine may be a major factor in determining heat sensitivity of Chinese hamster cells.

MEASUREMENT OF DNA CROSSLINKS BY S1 NUCLEASE: INDUCTION AND REPAIR IN PSORALEN‐PLUS‐360 nm LIGHT TREATED ESCHERICHIA COLI

Abstract: —DNA crosslinks in Escherichia coli cells. exposed to 4.5′,8-trimethylpsoralen plus 360 nm light, were measured using a rapid and sensitive new approach. The assay is based on the specificity of S1 nuclease from Aspergillus oryzae to single-stranded DNA. Bacterial cells were lysed and the DNA denatured by alkali. Following acid neutralization. crosslinked DNA undergoes spontaneous renaturation and is rendered S1-nuclease resistant and therefore acid-precipitable. The single-stranded fraction after denaturation by alkali decreases with increasing near UV light exposure in the presence of TMP following first order kinetics. The kinetics were faster when exposure was at 4°C rather than at 20°C. This suggests that excision of crosslinks occurs during exposure at the higher temperature. Indeed. since the rate of DNA crosslinking in a uvr B mutant which is excision-deficient was higher than in wild type bacteria at 4°C, some excision must have occurred even in the cold. DNA from excision-proficient cells incubated at 37°C following exposure to TMP-plus-near UV at 4° showed a greater single stranded fraction than that from non-incubated cells. This indicates repair of DNA crosslinks. which proceeded with a half-time of 8 min at 37°C and was unaffected by substitution of thymine in DNA by 5-bromouracil.

Dna damage and repair: induction and removal of thymine dimers in ultraviolet light irradiated intact water plants

Abstract: — The production of UV-induced thymine dimers and their fate upon post-irradiation incubation in the dark was studied in DNA of the intact water plants Wolffia microscopica and Spirodela polyrhiza. The results demonstrate production of thymine dimers, and the ability of the plant cells to remove the dimers from their DNA. The rate of removal is rapid during the first few h of post-irradiation incubation in the dark. It continues at a slower rate for the next 24–48 h, at which time it is essentially complete. The disappearance of thymine dimers in light or in the dark is analogous to the well-known processes in other biological systems, namely, photoreactivation and dark excision.

Enhancement of thermal killing by polyamines. II. Uptake and metabolism of exogenous polyamines in hyperthermic Chinese hamster cells.

Abstract: The uptake and metabolism of the polyamines spermine, spermidine, cadaverine and putrescine, previously shown to potentiate heat sensitivity, were studied in cultured Chinese hamster cells. Heat (42 degrees C) causes enhanced uptake of exogenously supplied polyamines into the acid-soluble fraction of the cells. Putrescine is taken up exceptionally fast at 37 degrees C, about 10 times faster than its homologue, cadaverine. This uptake is slower at 42 degrees C. The polyamines taken up were metabolized to some extent and the metabolites were similar at 37 degrees C and 42 degrees C except in the case of putrescine. These results suggest that potentiation of heat-sensitivity is probably mediated by the polyamines as such and not by their metabolites. Polyamines slightly protect the cells against the inhibitory effect of heat on RNA and protein synthesis. It is suggested that exogenous polyamines interact with nucleic acids inside the cell, and this interaction may underlie their synergism with heat. The exact nature of this interaction and the way it leads to enhanced thermal sensitivity are still obscure.

Photochemistry and photobiology of psoralens.

Abstract: — The photochemistry and photobiology of psoralens have been rcvicwed on the basis of selected literature. In addition to the well establishcd photoaddition of psoralens to DNA. photoreac-tions involving RNA. tRNA and proteins warrant further studies. Although thymine seems to be one of the predominant bases for the psoralen photocycloaddition in DNA. photoreactions of other bases such as adenine and the mechanisms other than cycloaddition should also be investigated in order to fully assess the specificity of psoralen photoreactions and their application BS a probe for biopolymer structure and as a tool for photobiological studies of microorganisms. The relativc photobiological importance of monoaddition vs crosslinking of psoralens to nucleic acids also remains to be fully elucidated.

Photodegradation of pharmaceuticals in the aquatic environment: A review

Abstract: A review with 310 references. Photochemical degradation is likely to be an important loss mechanism for many pharmaceutical pollutants in surface waters. This review summarizes the current knowledge of the photochemical behavior of pharmaceuticals and highlights the use of the fundamental photochemistry and phototoxicity literature to help understand and predict the aquatic fate of pharmaceuticals. Naproxen and diclofenac are shown to exemplify the idea that photochemical behavior obtained from fundamental photochemistry studies can be related to environmental conditions. There are, however, numerous compounds that have been found in environmental matrices for which no photochemistry data relatable to environmental conditions are available. It will be necessary to combine the results available in the large body of fundamental photochemistry and phototoxicity literature with laboratory and field experiments designed to determine direct and indirect photolysis rates and to identify photoproducts. This course will lead to a thorough understanding of the role of photodegradation on the fate and impact of pharmaceutical pollutants.

UV-B-Inducible and Temperature-Sensitive Photoreactivation of Cyclobutane Pyrimidine Dimers in Arabidopsis thaliana.

Abstract: Removal of cyclobutane pyrimidine dimers (CBPDs) in vivo from the DNA of UV-irradiated eight-leaf seedlings of Arabidopsis thaliana was rapid in the presence of visible light (half-life about 1 hour); removal of CBPDs in the dark, presumably via excision repair, was an order of magnitude slower. Extracts of plants contained significant photolyase in vitro, as assayed by restoration of transforming activity to UV-irradiated Escherichia coli plasmids; activity was maximal from four-leaf to 12-leaf stages. UV-B treatment of seedlings for 6 hours increased photolyase specific activity in extracts twofold. Arabidopsis photolyase was markedly temperature-sensitive, both in vitro (half-life at 30°C about 12 minutes) and in vivo (half-life at 30°C, 30 to 45 minutes). The wavelength dependency of the photoreactivation cross-section showed a broad peak at 375 to 400 nm, and is thus similar to that for maize pollen; it overlaps bacterial and yeast photolyase action spectra.

The Phthalocyanines: A New Class of Mammalian Cells Photosensitizers with a Potential for Cancer Phototherapy

Abstract: SummaryPhthalocyanines, porphyrin-like compounds with maximum absorption in the red, which were previously reported to localize selectively in tumours, have been shown to be efficient photosensitizers of mammalian cells in culture, thus making them possible candidates to replace haematoporphyrin derivatives in cancer phototherapy.