Brief exposure of yeasts to low-intensity monochromatic light (400-730 nm) has revealed the effects of photoreactivation and photoprotection of the cells inactivated by medium wave UVB radiation ...(290-320 nm). The red spectral region with a maximum at 680 nm has been found to be the most active in the initiation of photoreactivation and photoprotection. It has been noted that, according to the regularities investigated, these processes differ fundamentally from the known processes of enzymatic photoreactivation and photoprotection, which have a spectral response limited by, respectively, blue (< 450 nm) and near (< 380 nm) UV light. The data obtained make possible to consider the observed effects of photoreactivation and photoprotection as the manifestation of functioning of some light-dependent defense system capable of increasing the resistance of cells to UVB radiation.
The 2,2'-dipyridyl-induced accumulation of protoporphyrin IX in Saccharomyces cerevisiae cells was shown to be accompanied by the photoinhibition of cell respiration and the enhancement of the ...photoinduced permeability of plasma membranes to the fluorescent dye primuline. The visible-light illumination (at 400-600 nm) of the mitochondria and plasma membranes isolated from yeast cells with a high level of endogenous protoporphyrin IX intensified lipid peroxidation in these subcellular organelles. Comparative studies showed that the rad 52 mutant cells, which are deficient in the postreplicative recombinational DNA repair system, are considerably more sensitive to the inactivating action of visible light than are the wild-type cells and the rad 3 mutant cells, which are deficient in the excision DNA repair system. The contribution of photodynamic damage to the yeast subcellular organelles to the lethal photodynamic effect is discussed.
Yeast Saccharomyces cerevisiae accumulate in the presence of chelator 2,2'-dipyridyl, two fractions of photosensitizer protoporphyrin IX, which fluoresce with maxima at 625 and 635 nm. The two ...fractions were found to differ from each other in the dynamics and character of fluorescence photobleaching. In contrast to the protoporphyrin IX that fluoresces with a maximum at 625 nm, the protoporphyrin IX fraction that fluoresces with a maximum at 635 nm is more photolable; in addition, upon photobleaching of its fluorescence, a new maximum at 675 nm appears.
NADH-photosensitized in vitro formation of single-stranded breaks in plasmid DNA pBR322 depends on both the concentration of the sensitizer and the influence of near-UV radiation (320-400 nm). ...Scavengers and inhibitors of different activated oxygen species (sodium azide, sodium benzoate, catalase and superoxide dismutase) prevent the formation of breaks in full or partly. The data obtained show that hydroxyl radical (.OH) and singlet oxygen (1O2) are directly involved in the induction of breaks. In this process hydrogen peroxide (H2O2) plays the role of an intermediate in the reaction of .OH formation from superoxide anion-radical (O2-.) which is the first NAD.H-photogenerated product.
Dialyzed soluble proteins of Propionibacterium freudenreichii subsp. shermanii cell extract (dialyzate) were found to exert a protective and reactivating effect on Candida guilliermondii and ...Escherichia coli cells inactivated by UV light of C and B ranges. Reactivation occurred when dialyzate was added to irradiated bacterial suspensions immediately after irradiation or 15 min afterwards. Some common features of dialyzate effect on irradiated prokaryotic and eukaryotic cells were established. No reactivation was observed when the cells were irradiated with the light of visible (400-600 nm) or entire optical (> 290 nm) ranges. The possible mechanisms of a reactivating effect of dialyzate are discussed.
The fluorescence with maximum at 683 nm from isolated yeast plasma membranes has been detected. The fluorescence was due to a membrane-bound compound absorbing in the visible range of the spectrum. ...The fluorescence excitation spectrum of this compound has a structure typical for porphyrins. At the same time, in several fluorescence properties the porphyrin localized in the plasma membrane is different from other intracellular porphyrins (protoporphyrin, coproporphyrin).
It has been shown that NADH photosensitize in vitro single-strand breaks formation in double-strand plasmid DNA pBR 322 upon near-UV (320-400 nm) irradiation. The number of single-strand breaks ...depends both on UV light dose and sensitizer concentration. Addition of catalase and sodium benzoate strongly decreases the single-strand breaks formation. The results show an important role of hydrogen peroxide (H2O2) and hydroxyl radical (.OH) in inducing single-strand breaks in plasmid DNA irradiated by near-UV radiation in the presence of NADH.
Using two-dimensional thin-layer chromatography, the effect of serotonin on the yield of thymine dimers and on cleavage of the N-glycosidic bond in the DNA irradiated with ultraviolet (UV) light and ...X-ray was studied. Bound serotonin was shown to reduce the synthesis of UV-induced thymine dimers but had no effect on the number of X-ray-induced breaks in the N-glycoside bonds in thymidine residues. The data obtained are discussed in terms of the mechanisms of serotonin involvement in the photoprotection of yeast cells from the lethal action of UV and X-ray irradiations.
Long-wave (320-400 nm) UV-induced oxygen superoxide anion radical (O2-) formation was found in yeast cells. This radical plays an important part in initiation of photodestruction reactions in DNA ...which serves as a main target of UV irradiation in yeast. The observed cell photoinactivation spectrum at the wavelengths 320-400 nm suggests that NADH can serve as an endogenous sensitizer of O2- formation.
