PHOTOREACTIVATION and EXCISION REPAIR OF UV INDUCED PYRIMIDINE DIMERS IN THE UNICELLULAR CYANOBACTERIUM GLOEOCAPSA ALPICOLA (SYNECHOCYSTIS PCC 6308)

Abstract— The survival curve obtained after UV irradiation of the unicellular cyanobacterium Synecho-cystis is typical of a DNA repair competent organism. Inhibition of DNA replication, by incubating cells in the dark, increased resistance to the lethal effects of UV at higher fluences. Exposure of irradiated cells to near ultraviolet light(350–500 nm) restored viability to pre-irradiation levels. In order to measure DNA repair activity, techniques have been developed for the chromatographic analysis of pyrimidine dimers in Synechocystis. The specificity of this method was established using a haploid strain of Sacchar-omyces cerevisiae. In accordance with the physiological responses of irradiated cells to photoreactivating light, pyrimidine dimers were not detected after photoreactivation treatment. Incubation of irradiated cells under non-photoreactivating growth conditions for 15 h resulted in complete removal of pyrimidine dimers. It is concluded that Synechocystis contains photoreactivation and excision repair systems for the removal of pyrimidine dimers.     

OCCURRENCE OF PYRIMIDINE-RICH TRACTS IN ASCITES TUMOR DNA AND THE FORMATION OF UV-INDUCED THYMINE DIMERS

Abstract— Analysis of the distribution of pyrimidine-rich tracts (up to decanucleotides) in ascites tumor DNA revealed that these tracts occur predominantly in repetitive sequence of DNA. UV irradiation of ascites DNA resulted in preferential formation of thymine dimers in the pyrimidine-rich tracts as compared to other regions of DNA.     

ROLE OF COMPLEX FORMATION IN THE PHOTOSENSITIZED DEGRADATION OF DNA INDUCED BY N'-FORMYLKYNURENINE

Abstract— N'-Formylkynurenine derivatives efficiently bind to DNA or polynucleotides. Homopolynucleotides and DNA display marked differences in the binding process. Association constants are derived which indicate that the oxidized indole ring is more strongly bound to DNA than the unoxidized one. Irradiation of such complexes with wavelengths greater than 320 nm induces pyrimidine dimer formation as well as DNA chain breaks. Complex formation is shown to play an important role in these photosensitized reactions.
The photodynamic action of N'-formylkynurenine on DNA constituents is negligible at neutral pH but guanine and xanthine derivatives are sensitizable at higher pH. Thymine dimer splitting can occur in aggregated frozen aqueous solutions of N'-formylkynurenine and thymine dimer but this photosensitized splitting is negligible in liquid solutions at room temperature.     

NEAR ULTRAVIOLET AND POSTIRRADIATION DNA DEGRADATION: EFFECTS ON THE INDUCIBLE INHIBITOR OF IONIZING RADIATION-INDUCED DNA DEGRADATION

Abstract— Possible effects of near ultraviolet radiation (near UV) on DNA degradation were examined. Postirradiation DNA degradation induced by ionizing radiation in strain B_s-l ( uur-, lex- ) is shown to be inhibited by carbon monoxide (CO) and potassium cyanide (KCN) if the cells are grown on glycerol. Presumably the blockage of respiration by these agents lowers the amount of ATP in the cell. 50 kJ/m² near UV did not simulate the action of CO and KCN, indicating that at this Ruence the supply of ATP remains adequate for postirradiation DNA degradation. Near UV did not, itself, produce DNA degradation. In a strain (B/r) in which an inhibitor of postirradiation DNA degradation can be induced by both UV and ionizing radiation, near UV affects the inhibitor formation, whether administered before or after induction.     

UV-INDUCED DAMAGE OF PHOTORECEPTOR PROTEINS IN THE PARAFLAGELLAR BODY OF Euglena gracilis

Abstract— The paraflagellar body (PFB), the putative photoreceptor for phototaxis in the flagellate Euglena gracilis , was isolated still attached to the flagellum. After solubilization the proteins were separated and analyzed by two-dimensional gel electrophoresis. To discriminate the PFB-specific proteins from the flagella proteins, flagella without PFB were analyzed, isolated from the flagellate Astasia longa (a chlorophyll-free relative of E. gracilis ), which has no PFB and lacks phototaxis. The absorption spectra of solubilized PFB samples showed a maximum at 415 nm, two shoulders around 380 and 410 nm and two additional small peaks at 515 and 540 nm not present in the control sample without PFB. Two-dimensional gel electrophoresis showed eight PFB-specific proteins with molecular masses in the range of 25000–45000 and isoelectric points in the range of pH 3.5–7. Ultraviolet radiation strongly affects some of these PFB-specific proteins, but also flagella proteins are damaged by UV treatment. There is also a drastic decrease in the PFB-specific absorption maxima after UV irradiation.     

INHIBITION OF UV-INDUCED DNA STRAND BREAKAGE IN DICTYOSTELIUM DISCOIDEUM BY 2,4–DINITROPHENOL

Abstract— In UV-irradiated vegetative cultures of the cellular slime mold Dictyostelium discoideum NC-4, single strand breaks appeared in the DNA very rapidly and at low temperatures (0–4°C). However, when these cells were incubated, prior to UV irradiation, in the presence of 2 m M 2,4-dinitrophenol (DNP), an uncoupler of oxidative phosphorylation, breaks did not appear in the DNA. Extracts prepared from cells that had been incubated either in the presence or absence of DNP were tested for endonucleolytic activities on a UV-irradiated exogenous DNA template (φX-174 RF I). Results suggested that DNP might mediate its effect by interfering with the action of a UV-specific endonuclease.     

TOPICAL UROCANIC ACID ENHANCES UV-INDUCED TUMOUR YIELD AND MALIGNANCY IN THE HAIRLESS MOUSE

Epidermal urocanic acid has been postulated to be the mediator of the specific state of immunosuppression induced by UV irradiation, by which UV-initiated tumour cells are able to evade normal recognition and can survive to grow progressively into malignant tumours. These experiments demonstrate that topical application of UV-irradiated urocanic acid systemically suppresses the contact type hypersensitivity response to oxazolone in hairless mice. In addition, topically applied urocanic acid markedly increases the overt tumour yield and the degree of malignancy in hairless mice exposed chronically to daily minimally erythemal doses of simulated solar UV light. Topical urocanic acid also increases the number of latent UV-initiated tumours, detectable by croton oil promotion. Therefore UV photoproducts of urocanic acid can both systemically suppress contact hypersensitivity in the epidermis, and also enhance early survival of UV-initiated tumour cells resulting in augmentation of UV photocarcinogenesis.     

UV-INDUCED ALKALINE LABILE DNA DAMAGE IN HUMAN ADENOVIRUS AND ITS REPAIR AFTER INFECTION OF HUMAN CELLS

Abstract— UV-induced alkaline labile viral DNA damage was detected following irradiation of adenovirus type 2 and found to be repaired following the infection of human KB cells. Human adenovirus type 2 was irradiated with various doses of UV and subsequently used to infect human KB cells in tissue culture at approximately 2 × 10³ particles per cell. Before, and at various times after infection, the viral DNA was examined on alkaline sucrose gradients. Irradiated free virus DNA showed a dose dependent decrease in molecular weight compared to unirradiated virus DNA, indicating the presence of UV-induced alkaline labile lesions. Furthermore, an increase in the molecular weight of the irradiated virus DNA was found after infection indicating that alkaline labile lesions were removed from the viral DNA by a host mediated repair mechanism. After infection, the molecular weight of the irradiated virus DNA reached a value similar to that of unirradiated virus DNA for all the UV doses studied.     

WEIGLE-REACTIVATION IN A CYANOBACTERIUM (Synechococcus PCC7934) IS INDUCED BY UV BUT NOT BY MITOMYCIN-C OR NALIDIXIC ACID

Abstract— The cyanobacterium Synechococcus PCC7943 (Anacystis nidulans 602) exhibited UV induced Weigle-reactivation of irradiated cyanophaseAs–1. Weigle-reactivation had a half-life of approximately 34 min. It was not induced by treatments with the SOS inducing agents mitomycin-C or nalidixic acid.     

ACTION SPECTRA FOR ACCUMULATION OF INORGANIC CARBON IN THE CYANOBACTERIUM, Anabaena variabilis

Abstract— Action spectra for accumulation of inorganic carbon were obtained for Anabaena variabilis , strainM–2, in the presence and absence of photosynthetic CO₂ fixation. The action spectrum for inorganic carbon accumulation in the presence of CO₂ fixation showed a peak around 684 nm, corresponding to chlorophyll a absorption in PS 1, while that for CO₂ fixation showed a peak around 630 nm, corresponding to phycocyanin absorption in PS 2. The action spectra obtained in the presence of iodoacetamide or diuron, which inhibit CO₂ fixation, showed two peaks, one at about 684 nm and the other at 630 nm, with the 630 nm peak height 80 to 90% of the 684 nm peak. These results indicate that inorganic carbon transport in A. variabilis can be driven with near equal efficiency by energy derived from absorption in photosystem 1 alone and with energy transferred to PS 1 after absorption by PS 2.     

WAVELENGTH DEPENDENCE AND KINETICS OF UV-INDUCED FREE RADICAL FORMATION IN THE HUMAN CORNEA AND LENS

Abstract— The wavelength dependence of free radical formation in the human lens and cornea was obtained in the ultraviolet-visible (UV-VIS) range with electron paramagnetic resonance. The spectral feature of having their maxima close to 290 nm, negligible intensity above 320 nm, and appreciable intensity toward 260 nm is common to both of these tissues.
The kinetics of free radical formation in the lens and cornea was interpreted in terms of a two component exponential function with characteristic rate constants k _l and k ₂, the latter of which has the same value for both the lens and cornea.     

QUANTITATIVE ASPECTS OF POLYMER DEGRADATION IN THE LIVING BODY

Abstract

Over the last several decades extensive clinical research has been devoted to the medical application of polymeric implants. Scientists in the last few years have paid special attention to the chemical physics of the processes that accompany the reaction of polymers with living tissue. Two main questions must first be answered in this type of study.     

SPECTRAL DEPENDENCE OF UV-INDUCED IMMEDIATE AND DELAYED APOPTOSIS: THE ROLE OF MEMBRANE AND DNA DAMAGE

Abstract— The phototoxicity of each waveband region of UV radiation (UVR), i.e., UVA (32CM100 nm), UVB (290–320 nm) and UVC (200–290 nm), was correlated with an apoptotic mechanism using equilethal doses (10% survival) on murine lymphoma L5178Y-R cells. Apoptosis was qualitatively monitored for DNA "ladder" formation (multiples of 200 base pair units) using agarose gel electrophoresis, while the percentages of apoptotic and membrane-permeabilized cells were quantified over a postexposure time course using flow cytometry. The UVA1 radiation (340–400 nm) induced both an immediate (<4 h) and a delayed (>20 h) apoptotic mechanism, while UVB or UVC radiation induced only the delayed mechanism. The role of membrane damage was examined using a lipophilic free-radical scavenger, vitamin E. Immediate apoptosis and membrane permeability increased in a UVA1 dose-dependent manner, both of which were reduced by vitamin E. However, vitamin E had little effect on UVR-induced delayed apoptosis. In contrast, the DNA damaging agents 2,4- and 2,6-diaminotoluene exclusively induced delayed apoptosis. Thus, immediate apoptosis can be initiated by UVA 1-induced membrane damage, while delayed apoptosis can be initiated by DNA damage. Moreover, the results suggest that immediate and delayed apoptosis are two independent mechanisms that exist beyond the realm of photobiology.     

UV-INDUCED PROTEIN ALTERATIONS AND LIPID OXIDATION IN ERYTHROCYTE MEMBRANES

Certain ultraviolet radiation-induced effects in skin may result from primary photochemical alterations in cell membranes. We have studied isolated erythrocyte membranes in order to determine the UV-fluence and wavelength dependence for protein alterations and lipid oxidation. Protein crosslinking was detected as high molecular weight protein (greater than 200,000 DA) on polyacrylamide/agarose gel electrophoresis. Spectrin decreased more rapidly than the other membrane proteins upon exposure to lambda = 250-380 nm radiation. Nitrogen-purging inhibited the UV-induced decrease in spectrin by 60% and decreased crosslinking to an even greater degree. The decrease in spectrin was not inhibited by superoxide dismutase, catalase, or sodium azide. Radiation at 280 nm was most effective for spectrin loss, 265 and 297 nm were less effective and 254 and 313 nm were not effective. Prior irradiation at 280 nm did not sensitize the membranes to subsequent irradiation at 313 nm indicating that photodecomposition products of tryptophan are not involved. Lipid photooxidation was measured with the thiobarbituric acid assay and was induced at higher fluences of UV radiations than those required for loss of spectrin. These results indicate that the major effects of UV radiation on cell membranes are alterations of proteins and suggest that tryptophan is the major chromophore for these alterations.     

THE ROLE OF HUMIC SUBSTANCES IN THE PHOTOCATALYTIC DEGRADATION OF WATER CONTAMINANTS

Abstract

Photocatalysis over irradiated Ti0₂ has been proved to efficiently abate more than 80% of the organic carbon pertaining to a commercial humic acid (HA). The presence of HA up to 50 mg L^?1 has been found to decrease the degradation rate of some model pollutants, namely phenol, 2,4-dichlorophenol and tetrachloromethane. However, the total organic carbon measurements and chloride evolution ensure that the disappearance of the initial pollutants is not due to binding to HA structure, but to an efficient mineralization process. HA' s are able to scavenge both the oxidative and the reductive active species as shown by the inhibiting effect on the rate of disappearance of phenol and 2,4-dichlorophenol (essentially oxidative), and of CCI4 (initially reductive).     

THE N-NITROSAMINES IN TOBACCO SMOKE AND ITS ADSORPTION AND DEGRADATION

1. INTRODUCTION Tobacco smoking ranks as a major public health problem whose negative impacts have been well established since the report of “smoking and health” published by the royal medicine academy of English in 1954. Besides nicotine, the major inducer of tobacco dependence, cigarette smoke also contains various toxic compounds, notably N-nitrosamines. Nitrosamines are formed by the nitrosation(addition of an N=O group, from the nitroso ramifications NO2, N2O3,N2O4) of secondary…     

THE ROLE OF UROCANIC ACID IN UV-INDUCED IMMUNOSUPPRESSION: RECENT ADVANCES (1992–1994)

Abstract— Cis - urocanic acid (UCA), formed in the epidermis by UV irradiation of trans-UCA , has been implicated as a mediator of the immunosuppression induced by UV exposure of the skin. This review covers recent work in which the wavelength dependence of cis-UCA formation, the interaction of UCA isomers with DNA, the effects of UCA isomers on the immune system and their interaction with histamine are examined. Results are frequently conflicting, particularly when considering the possible mode of action of cis -UCA but, overall, a multifaceted role for UCA in immunomodulation by UV radiation is substantiated.     

A SEROLOGICAL STUDY OF REMOVAL OF UV-INDUCED PHOTOPRODUCTS IN THE DNA OF TETRANYMEN A PYRIFORMIS GL: INFLUENCE OF CAFFEINE, QUINACRINE AND CHLOROQUINE

Abstract—Antisera that recognize specifically UV-photoproducts in DNA have been used to follow the elimination of photolesions in UV irradiated Tetrahymena pyriformis . The amount of bound tritiumlabelled antibodies to nuclei has been estimated by autoradiography. Curves of dose-response of DNA photoproducts, their elimination by dark repair, and effect of caffeine, quinacrine and chloroquine on the disappearance of UV-lesions have been evaluated.     

STATE I-STATE II TRANSITIONS IN THE THERMOPHILIC BLUE-GREEN ALGA (CYANOBACTERIUM) Synechococcus lividus*

Time courses of state I-state II transitions were measured in the thermophilic blue-green alga (Cyanobacterium), Synechococcus lividus, that was grown at 55°C. The rate of the state I–II transition using light II illumination was the same as that in the dark, and the dark state was identified to be state II. Therefore, light regulation attained by state transitions is produced by the state II–I transition induced by system I light. The redox level of plastoquinone did not affect this dark state II. Arrhenius plots of the state transitions showed a break point around 43°C that corresponded to the phase transition temperature of this alga. Since both the state I–II and II–I transitions were very much temperature-independent, we could keep the alga in either state for a long time at a “low” temperature such as room temperature. Activities of both photosystems I and II in states I and II were also measured. After a state II–I transition, the system II activity increased about 16% and at the same time, svstem I activity decreased about 30%.     

THE N-NITROSAMINES IN TOBACCO SMOKE AND ITS ADSORPTION AND DEGRADATION

N-nitrosamines are strong carcinogens for humans. This paper gives an overview of the nitrosmaines in cigarette smoke including the formation, the harmfulness, the analytical methods of the nitrosmaines and the adsorptions and degradations of N -nitrosamines.