[New photo-induced effects of reactivation and protection of yeast cells under lethal UVB radiation].

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.

[Photodynamic damage of yeast subcellular fraction induced by elevated levels of endogenous protoporphyrin IX]. / Fotodinamicheskoe povrezhdenie subkletochnykh struktur drozhzhei s indutsirovannym nakopleniem éndogennogo protoporfirina IX.

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.

[Fluorescent photobleaching of endogenous protoporphyrin IX in yeast cells]. / Fotovytsvetanie fluorestsentsii éndogennogo protoporfirina IX v drozhzhevykh kletkakh.

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.

[Study of fluorescence from isolated yeast plasma membranes in visible range of the spectrum]. / Issledovanie fluorestsentsii izolirovannykh plazmaticheskikh membran drozhzhei v vidimoi oblasti spektra.

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).

[Protective and reactive effect of a cellular extract from propionic acid bacteria on Candida guilliermondii and Escherichia coli, inactivated by ultraviolet radiation]. / Protektornoe i reaktiviruiushchee deistvie kletochnogo ékstrakta propionovo-kislykh bakterii na Candida guilliermondii i Escherichia coli, inaktivirovannye ul'trafioletovym izlucheniem.

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.

[Mechanism of NADH-sensitized formation of DNA breaks during irradiation with near UV light]. / Izuchenie mekhanizma NADH-sensibiliziruemogo obrazovaniia razryvov v DNK pri obluchenii blizhnim UF-svetom.

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.

[Sensitized NADH formation of single-stranded breaks in plasmid DNA upon the action of near UV-radiation]. / Sensibilizirovannoe NADH obrazovanie odnonitevykh razryvov v plazmidnoi DNK pri deistvii blizhnego UF-izlucheniia.

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.

[A photosynergistic lethal effect in the irradiation of yeasts with long-wave ultraviolet and visible light]. / Fotosinergicheskii letal'nyi éffekt pri obluchenii drozhzhei dlinnovolnovym ul'trafioletovym i vidimym svetom.

A lethal synergistic effect which is expressed as the nonadditive summing of the damaging effect of each irradiation separately has been found during the investigation of combined action of longwave ultraviolet (UV) rays (337 nm or 365 nm) and visible light (400-600 nm) on the yeast cells. Based on the data on different mechanisms of lethal effect of longwave UV and visible light, it has been suggested that the basis of the photosynergistic effect is the mutual intensification of the photo-destructive processes occurring in different intracellular structures and processes induced by different endogenous sensitizers.

[Photogeneration of the superoxide anion oxygen radical and its role in the inactivation of yeast cells by long-wave UV light]. / Fotogeneratsiia superoksidnogo anion-radikala kisloroda i ego rol' v inaktivatsii kletok drozhzhei dlinnovolnovym UF-svetom.

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.

[Competitive interaction of serotonin and the dye acridine orange with DNA]. / Konkurentnoe vzaimodeistvie serotonina i krasitelia akridinovogo oranzhevogo s DNK.

The interaction of serotonin and acridine orange dye with DNA isolated from bacterium Escherichia coli and the yeast Candida utilis has been analysed by spectrofluorimetric method. Using data on competitive binding to DNA of serotonin and acridine orange, known as DNA intercalator, a conclusion concerning the formation of intercalated complex between serotonin and DNA has been made. It is shown that for yeast DNA the constant of intercalated binding of serotonin is 3,5-fold smaller than for the bacterial one.

[Effect of serotonin on the yield of UV- and x ray-induced DNA damage]. / Vliianie serotonina na doliu indutsirovannykh ul'trafioletovym svetom i rentgenovskim oblucheniem povrezhdenii v DNK.

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.

[Effect of serotonin on the yield of UV-induced thymine dimers in DNA]. / Vliianie serotonina na vykhod UF-indutsirovannykh timinovykh dimerov v DNK.

Using a fluorescence method the interaction between serotonin and DNA has been investigated and the association constant Kc = 4.2 X 10(4) M-1 was determined. Bound serotonin is shown to reduce the yield of UV-induced thymine dimers in DNA. It is calculated that the value of the effective distance over which each protector acts is a segment of the DNA helix about four base pairs long.

[Role of DNA damage in the inactivation of Saccharomyces cerevisiae yeasts by 313-nm ultraviolet light]. / Rol' povrezhdeniia DNK v inaktivatsii drozhzhei Saccharomyces cerevisiae ul'trafioletovym svetom 313 nm.

The relative contribution of respiration photoinhibition and DNA damage in the lethal effect induced by 313 nm ultraviolet light (UV) has been investigated in some strains of the yeast Saccharomyces cerevisiae. It has been shown that cells inactivation is essentially due to photo-induced damage to DNA. By photoreactivation experiments it has been found that dimers of the pyrimidine bases are the main lethal photoproducts induced in the DNA by 313 nm ultraviolet light.

[Effect of the photo-induced synthesis of serotonin on the photoreactivation of Saccharomyces cerevisiae yeasts]. / O vliianii fotoindutsirovannogo sinteza serotonina na fotoreaktivatsiiu drozhzhei Saccharomyces cerevisiae.

The photoreactivation of yeast (Saccharomyces cerevisiae) cells irradiated by far-UV-light has been studied. It has been shown that the near-UV-induced (334, 365 nm) synthesis of serotonin in yeast is an underlying cause of its photoreactivation action spectrum change. The effect of serotonin is due to its binding to far-UV-irradiated DNA (pyrimidine dimers) making them unavailable to the photoreactivating enzyme. The data obtained support the idea that serotonin affects the repair enzymes which are engaged in an elimination of lethal photoproducts from DNA.

[Concurrent effect of ultraviolet rays of various wave lengths on Saccharomyces cerevisiae survival]. / Konkurentnoe deistvie ul'trafioletovykh luchei raznoi dliny volny na vyzhivaemost' Saccharomyces cerevisiae.

While studying the combined action of different UV wavelengths on Saccharomyces cerevisiae (strains XII and Cl-9), it has been found that preliminary irradiation with UV at 334 nm caused photoprotection of the cells against the lethal action of UV at 254 and 313 nm. Postradiation irradiation of strain XII incapable of photoreactivation with UV at 334 nm increased the lethal action of UV at 254 and 313 nm. The mechanisms of the both effects are based on serotonin synthesis induced by the light at 334 nm, as was shown using p-chlorophenylalanine, a specific inhibitor of serotonin synthesis. In strain CI-9 capable of photoreactivation, the postradiation effect of the light at 334 nm depends on the interaction of two different photobiological reactions induced by it, namely, photoreactivation and induced serotonin synthesis.