ENHANCEMENT OF ULTRAVIOLET OR N-METHYL-N'- NITRO-N-NITROSOGUANIDINE SENSITIVITY OF DICTYOSTELIUM DISCOIDEUM BY 3-AMINOBENZAMIDE

Abstract— The amoeboid cells of Dktyostelium discoideum NC–4 possess a 3-aminobenzamide(3-ABA)-sensitive repair mechanism for DNA damages induced by UV-irradiation or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-treatment. We have studied the effect of 3-ABA on each step of excision repair in the UV- irradiated cells. Although the nicking of DNA-strand and the excision of pyrimidine dimcrs are insensitive to 3-ABA, the rejoining of DNA strand-breaks is sensitive. The frequency of mutation induced by UV-irradiation or MNNG-treatment is depressed by 3-ABA. The mechanisms of repair inhibition by 3-ABA are discussed.     

EFFECT OF GROWTH TEMPERATURE ON LIPID COMPOSITION and ULTRAVIOLET SENSITIVITY OF HUMAN CELLS

Human skin fibroblasts were incubated at either 25 or 37 degrees C before UV irradiation. Cells incubated at 25 degrees C were more resistant to near UV radiation than cells grown at 37 degrees C, but cells grown at the lower temperature were more sensitive to 254 nm radiation. Fatty acid analysis of membranes of cells showed that cells incubated at the lower temperature contained significantly higher amounts of linoleic acid (18:2) and linolenic acid (18:3) than cells incubated at 37 degrees C. To determine if this difference in fatty acid content of the membranes was responsible for the UV survival characteristics of cells incubated at different temperatures, cells were enriched with either linoleate or linolenate during a 37 degrees C incubation period. Gas chromatography revealed that cells incorporated the supplied fatty acid. Fatty acid enriched cells were then irradiated with near UV, and survival characteristics were compared to those obtained with cells grown at the lower incubation temperature. The results suggest that the different proportion of fatty acid content of the cells is not the cause of different UV sensitivities of cells grown at 25 degrees C compared to cells grown at 37 degrees C.     

ULTRAVIOLET SENSITIVITY OF THE ADDITION, DELETION and REPLACEMENT OF LONG NONHOMOLOGOUS DNA SEGMENTS BY GENETIC TRANSFORMATION OF HAEMOPHILUS INFLUENZAE

Abstract— We have recently described the construction and some properties of Haemophilus influenzae Rd strains with long and different R plasmid-derived DNA segments (nonhomologous inserts) at the same site in the HP1 prophage. These inserts can be added to a recipient's genome by genetic transformation, they can be deleted from the recipient genome, or they can be replaced by another insert. We report here that the UV inactivation of all three phenomena followed single hit kinetics. Deletion was roughly 10 times more resistant; its UV-sensitivity equaled that of a high-efficiency point mutation. There was an inverse correlation between UV-sensitivity and additive transformation efficiency of the various inserts; sensitivity may thus be a measure of insert size. This correlation was not seen for deletion. All three phenomena were more sensitive when they were measured on excision repair-deficient uvr_- recipients. The dose-reduction factor for addition was about 1.5 while it was about 2.6 for deletion.     

SENSITIVITY OF MOUSE SKH:HR-2 TO ULTRAVIOLET LIGHT: MOUSE PIGMENTATION MODEL

Abstract— The mouse Skh:HR-2 has been reported to be sensitized to ultraviolet light and become pigmented. Using three independent parameters associated with pigmentation. we have examined the ability of the mouse to become pigmented. The methods utilized were spectroscopic (skin color). histological (melanocyte density and epidermal thickness), and biochemical (tyrosinase activity). Following a two-week ultraviolet exposure, the mice were pigmented with the degree of pigment change related to the ultraviolet dose administered. Perturbations in skin color, epidermal thickness, melanocyte density, and tyrosinase activity were recorded. Mice were also examincd for their response to tyrosinc applied topically following each ultraviolet exposure. With the exccption of epidermal thickness. all the pigmentation parameters were accentuated when compared to results from ultraviolet exposure alone.     

THE EFFECT OF CHANGES IN CELL GEOMETRY ON THE SENSITIVITY TO ULTRAVIOLET RADIATION OF MAMMALIAN CELLULAR CAPACITY

Abstract— We have measured a calcium and magnesium dependent change in cell shape when mammalian cell monolayers are being prepared for irradiation by replacing their growth medium with certain buffers. In some cases, flattened cells (umbonate) assumed a spherical configuration. In order to assume a centrally located target molecule, we used a DNA-dependent cellular function–pacity for herpes viral growth–as the parameter to measure ultraviolet (UV) sensitivity of cells irradiated while in either of the two shapes. Umbonate cells were more sensitive to UV than were spherical cells. Exposures to the cell that lowered the cellular capacity of umbonate cells to the 10% survival level only lowered spherical cells to the 50% level. Twenty-seven per cent additional UV exposure to spherical cells was required to get the same effect as with umbonate cells. Included in the text are photographs of both cell types, survival curves for cellular capacity, a measure of the absorbance of cell homogenates, and a calculation of the relative number of photons absorbed by each cell nucleus.     

A CLIMATOLOGY OF SUNBURNING ULTRAVIOLET RADIATION

Abstract— Data are presented from 14 sites where continuous measurements of the sun's shortest ultraviolet radiation reaching the earth's surface have been made for four or more years. Average daily dose per month and its variability from year to year is shown for each station. Some of the many influences affecting these measurements can be discerned by station intercomparisons. No consistent long term change in solar UV-B radiation reaching the ground is evident.     

ULTRAVIOLET IRRADIATION OF NUCLEIC ACIDS COMPLEXED WITH HEAVY ATOMS—III. INFLUENCE OF Ag + AND Hg 2+ ON THE SENSITIVITY OF PHAGE AND OF TRANSFORMING DNA TO ULTRAVIOLET RADIATION

Abstract— We have studied the influence of the heavy metal ions Ag⁺ and Hg²⁺ on the photoinactivation and photodimerization of transforming DNA and of bacteriophage. The rate of inactivation of Haemophilus influenzae transforming DNA by ultraviolet (UV) radiation was enhanced by a factor of 30 when it was complexed with Ag⁺. This enhancement was correlated with a comparable increase in the rate of thymine dimerization. In contrast, mercuric ions led to a reduction in the rates of both inactivation and dimerization. When we examined the effects of these metal ions on the photobiology of bacteriophage, we again found that Ag⁺ enhanced and Hg²⁺ reduced the rate of ultraviolet inactivation. These results demonstrate that heavy metals may be useful tools for studying the photochemistry and photobiology of nucleic acids.     

A LABORATORY INVESTIGATION OF TWO ULTRAVIOLET SPECTRORADIOMETERS

Abstract— Spectral measurements of the solar UV irradiance at the earth's surface depend critically on the characteristics of the spectroradiometers and the procedures used in their calibration. Two UV spectroradiometers were subjected to a series of laboratory tests to investigate which factors were most significant in limiting the reliability of the absolute irradiance measurements. Three independent standards of spectral irradiance were scanned by both instruments under a range of bench conditions. The results were consistent to within about 3%, most of the uncertainty being due to scattered light in the laboratory. An UV laser was used to determine the slit function of each spectrometer and the influence of internal stray light. Significant departures from the ideal cosine and azimuth responses were measured by a xenon lamp. Both spectroradiometers were kept indoors throughout the experiments. The relevance of these laboratory results is discussed with respect to the task of measuring solar UV radiation in the field.     

THE FUNCTION OF CAROTENOIDS IN A PHOTOCHROMOGENIC BACTERIUM*

Abstract— The role of carotenoids in protecting a photochromogenic Mycobacterium has been investigated. Bacteria previously induced to synthesize carotenoids by low intensity white light are not killed by high intensity white light while uninduced (carotenoid-free bacteria) are. If high intensity irradiation with white light is carried out at O°, carotenoids still protect these organisms although at a reduced level. This finding is taken to mean that carotenoids can protect these organisnis from photodynamic death by shading photosensitizing pigments.     

INACTIVATION OF A RHIZOBIUM BACTERIO-PHAGE BY ULTRAVIOLET RADIATION OF DIFFERENT WAVE-LENGTHS

Abstract— The action spectrum for inactivation of a Rhizobiurn bacteriophage by U.V. radiation follows the shape of the absorption spectrum of DNA between the wave-lengths of 240 and 290 mμ (where inactivation probably reflects damage to the nucleic acid only), and deviates sharply upwards at wave-lengths shorter than 240 mμ (where inactivation may depend on damage to both the nucleic acid, and protein of the phage). The rate of inactivation follows first order kinetics approximately at all wave-lengths tested. Infectivity of the phage is halved when each mg of the phage nucleic acid has absorbed about 0 08 J of radiation energy at any wave-length between 240 and 290 mμ.
The bacteriopharge can be photoreactivated after inactivation at any wave-length between 230 and 290 mμ, but less so after inactivation at 230 mμ than at any wave-length above 240 mμ. No evidence was found to suggest that dimerization of thymine residues of the phage-DNA plays any part in the mechanism of inactivation of the bacteriophage by U.V. radiation.     

A COMPARISON OF DOSIMETERS USED FOR SOLAR ULTRAVIOLET RADIOMETRY

Radiometric measurements of terrestrial sunlight using three different types of broad-band dosimeters were compared with equivalent integrated quantities obtained from simultaneous spectroradiometric measurements. Measurements were made at Durham, UK (55 degrees N) during one day in mid-summer and one day in the autumn. By this means it was possible to encompass a wide range of ultraviolet irradiances. There was close agreement between UV-A irradiance measured using a broad-band radiometer and determined spectroradiometrically over the whole range of irradiances when allowance was made for the spectral sensitivity of the UV-A radiometer. The agreement between erythemally-effective irradiance determined spectroradiometrically and the response of a Robertson-Berger meter showed some non-linearity due to the mismatch between the erythema action spectrum and spectral response of the sensor. There was a similar disparity in agreement between erythemally-effective dose determined spectroradiometrically and the response of polysulphone film for similar reasons. Nevertheless it is concluded that if these latter two dosimeters are calibrated using sunlight, or a solar simulator, as the source, they can yield data which are sufficiently reliable for many applications.     

PHOTOREACTIVATION OF ULTRAVIOLET IRRADIATED NON-DIVIDING POPULATIONS OF ICR 2A FROG CELLS

Abstract— Ultraviolet (UV) irradiation of non-dividing populations of ICR 2A frog cells led to their detachment from the surface of the culture dish and eventual lysis. Exposure of the cells to photoreactivating light after UV irradiation prevented cell killing and was accompanied by a loss of endonuclease sensitive sites from DNA. This photoreversal did not take place when the cells were exposed at 4°C to photoreactivating light indicating that the reversal was the result of photoenzymatic repair. As the action of photoreactivating enzyme is specific for the repair of pyrimidine dimers in DNA, these results suggest that pyrimidine dimers in DNA are the critical lesions leading to the death of non-dividing populations of UV irradiated cells.     

ULTRAVIOLET PHOTOLYSIS OF RIBOFLAVIN IN PYRIDINE: A PRELIMINARY STUDY

Abstract— Ultraviolet photolysis of riboflavin in pyridine leads to the formation of a red photoproduct. This photoreaction is apparently attributed to the photochemical interaction of pyridine with riboflavin. It is found that the rate of the photoreaction follows 1/2 order kinetics with respect to pyridine. ESR spectrum of the irradiated reaction mixture appears to be identical with that of riboflavin semiquinone obtained from visible light irradiation. Whether or not such a flavin radical is the responsible intermediate in the photoreaction is not established. Possible modes of the reaction are discussed. Absorption, excitation, and emission spectra of the red photoproduct strongly suggest that the structure of the photoproduct is considerably different from that of riboflavin or pyridine, indicating an extensive photolytic process involving covalent bond alterations.     

MEASUREMENTS OF SOLAR MIDDLE ULTRAVIOLET RADIATION IN A DESERT ENVIRONMENT

Abstract— In this study measurements are reported that were carried out between August 1983 and December 1985 on the solar middle ultraviolet radiation (UVB-280-320 nm) in Kuwait (29.5°N). These measurements are based primarily on polysulfone film detectors. Comparative measurements were also made on a Robertson-Berger meter and a spectroradiometer. The results reported include the daily variation of the solar UVB between 11:30 a.m. and 12:00 noon over the year, the diurnal variation, as well as the amount of UVB as a function of the receiving angle with the horizontal.
Based on these data the polysulfone films were found to be reliable and inexpensive detectors, giving results similar to those of the R-B meter. The diurnal variation of the solar UVB was found to vary as sin2q, where q is an angle that corresponds to the time since sunrise compared to the sunrise-sunset interval times 180. An empirical equation is developed that gives the maximum UVB as a function of the time of day and day of year. A correlation is determined of the polysulfone readings with the spectroradiometric and the R-B meter measurements. The solar insolation was found to be independent of the receiving angle with the horizontal in the winter months and develops into a cosine dependence in the summer months.     

WAVELENGTH DEPENDENCE OF DNA INCISION BY A HUMAN ULTRAVIOLET ENDONUCLEASE

The wavelength dependence of an ultraviolet irradiation of the DNA substrate for a human endonuclease was determined. Sites of DNA incision for all UVB and UVC wavelengths examined were at cytosines which were neither cyclobutane pyrimidine dimers nor 6-4'-(pyrimidin-2-one)pyrimidines. The optimal wavelengths for formation of these cytosine photoproducts were between 270 and 295 nm. This human endonuclease therefore has a similar ultraviolet substrate specificity to endonuclease III.     

CORRELATION BETWEEN ENDOGENOUS GLUTATHIONE CONTENT AND SENSITIVITY OF CULTURED HUMAN SKIN CELLS TO RADIATION AT DEFINED WAVELENGTHS IN THE SOLAR ULTRAVIOLET RANGE

Abstract— Glutathione depletion of cultured human skin fibroblasts by treatment with buthionine-S,R-sulfoximine (BSO) sensitises them to radiation at a series of defined wavelengths throughout the solar UV range. We now show that there is a close quantitative correlation between cellular glutathione content (as depleted by BSO) and sensitivity to radiation at 365 nm. A weaker correlation is observed when cells are depleted of glutathione using diethylmaleimide. Both fibroblasts and epidermal keratinocytes derived from the same foreskin biopsy are sensitised to radiation at 313 nm by glutathione depletion. However, the keratinocytes are sensitised to a much lesser extent, an observation which agrees quantitatively with the higher residual levels of cellular glutathione remaining after maximum depletion by BSO (approximately 25% for the keratinocytes vs less than 5% for the fibroblasts). At low to intermediate fluence levels, 10 mM cysteamine present during irradiation at 302 nm is able to almost completely reverse the sensitising effects of glutathione depletion suggesting that the endogenous thiol protects against radiation at this wavelength by a free radical scavenging mechanism. At 313 nm, the sensitisation is not reversed by cysteamine suggesting that glutathione plays a more specific role in protection against radiation at longer wavelengths. Xeroderma pigmentosum group A fibroblasts (excision deficient) are also sensitised to radiation at 313 and 365 nm by depletion of glutathione but since the sensitization is less than that observed for the normal strain, we cannot conclude that glutathione protects against a sector of DNA damage susceptible to excision repair. The results provide further evidence that endogenous glutathione is involved in protecting human skin cells against a wide range of solar radiation damage and suggest that while free radical scavenging is involved at the shortest wavelength (302 nm) tested, a more specific role of glutathione is involved in protection against radiation at longer wavelengths.     

高灵敏催化光度法测定痕量锰

研究了痕量Mn2 + 催化KIO4 氧化棉红的反应动力学 ,测定了反应级数、表观速率常数和表观活化能 ,确立了速率方程 ,探讨了反应机理 ,建立了测定痕量锰的方法 ,方法灵敏度为 7.5×10 - 9g·L- 1,线性范围为 0 .0～ 6.0× 10 - 6g·L- 1。方法选择性好 ,直接用于化学试剂、井水及蒸馏水中痕量锰的测定 ,结果满意