Ultraviolet radiation-mediated damage to cellular DNA.
ABSTRACT Emphasis is placed in this review article on recent aspects of the photochemistry of cellular DNA in which both the UVB and UVA components of solar radiation are implicated individually or synergistically. Interestingly, further mechanistic insights into the UV-induced formation of DNA photoproducts were gained from the application of new accurate and sensitive chromatographic and enzymic assays aimed at measuring base damage. Thus, each of the twelve possible dimeric photoproducts that are produced at the four main bipyrimidine sites can now be singled out as dinucleoside monophosphates that are enzymatically released from UV-irradiated DNA. This was achieved using a recently developed high-performance liquid chromatography-tandem mass spectrometry assay (HPLC-MS/MS) assay after DNA extraction and appropriate enzymic digestion. Interestingly, a similar photoproduct distribution pattern is observed in both isolated and cellular DNA upon exposure to low doses of either UVC or UVB radiation. This applies more specifically to the DNA of rodent and human cells, the cis-syn cyclobutadithymine being predominant over the two other main photolesions, namely thymine-cytosine pyrimidine (6-4) pyrimidone adduct and the related cyclobutyl dimer. UVA-irradiation was found to generate cyclobutane dimers at TT and to a lower extent at TC sites as a likely result of energy transfer mechanism involving still unknown photoexcited chromophore(s). Oxidative damage to DNA is also induced although less efficiently by UVA-mediated photosensitization processes that mostly involved 1O2 together with a smaller contribution of hydroxyl radical-mediated reactions through initially generated superoxide radicals.
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ABSTRACT: Photosensitized oxidations involve the generation of radicals (type I mechanism) and/or the production of singlet molecular oxygen (1O2) (type II mechanism). Phenalenone (PN) is one of the well-known type II photosensitizers and is widely used as a 1O2 reference sensitizer. In this work, we have studied the interaction of tryptophan (Trp) with the excited states of PN, the production of 1O2 in the presence of Trp, the formation of radicals and the kinetics of the photodegradation of Trp under different experimental conditions. In contrast to what is usually assumed, we have proven that PN is also able to act as a type I photosensitizer. Moreover, we have demonstrated that the predominant mechanism of the photosensitization of Trp by PN involves an electron transfer initiated-process.RSC Advances 01/2014; 4(21):10718. DOI:10.1039/c3ra46867d · 3.71 Impact Factor
Periodica Polytechnica Chemical Engineering 01/2015; DOI:10.3311/PPch.7290 · 0.13 Impact Factor
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ABSTRACT: The aim of our experiment Phage and Uracil Response was to extend the use of bacteriophage T7 and uracil biological dosimeters for measuring the biologically effective ultraviolet (UV) dose in the harsh extraterrestrial radiation conditions. The biological detectors were exposed in vacuum-tightly cases in the European Space Agency (ESA) astrobiological exposure facility attached to the external platform of Zvezda (EXPOSE-R). EXPOSE-R took off to the International Space Station (ISS) in November 2008 and was installed on the External platform of the Russian module Zvezda of the ISS in March 2009. Our goal was to determine the dose-effect relation for the formation of photoproducts (i.e. damage to phage DNA and uracil, respectively). The extraterrestrial solar UV radiation ranges over the whole spectrum from vacuum-UV (λ<200 nm) to UVA (315 nm<λ<400 nm), which causes photolesions (photoproducts) in the nucleic acids/their components either by photoionization or excitation. However, these wavelengths cause not only photolesions but in a wavelength-dependent efficiency the reversion of some photolesions, too. Our biological detectors measured in situ conditions the resultant of both reactions induced by the extraterrestrial UV radiation. From this aspect the role of the photoreversion in the extension of the biological UV dosimetry are discussed.International Journal of Astrobiology 01/2014; 14(01):47-53. DOI:10.1017/S1473550414000287 · 0.83 Impact Factor