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Ultraviolet light
About: Ultraviolet light is a research topic. Over the lifetime, 49494 publications have been published within this topic receiving 843151 citations.
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TL;DR: The PTEN tumour suppressor and pro-apoptotic gene is frequently mutated in human cancers and loss of Egr-1 expression could deregulate the PTEN gene and contribute to the radiation resistance of some cancer cells.
Abstract: The PTEN tumour suppressor and pro-apoptotic gene is frequently mutated in human cancers. We show that PTEN transcription is upregulated by Egr-1 after irradiation in wild-type, but not egr-1-/-, mice in vivo. We found that Egr-1 specifically binds to the PTEN 5' untranslated region, which contains a functional GCGGCGGCG Egr-1-binding site. Inducing Egr-1 by exposing cells to ultraviolet light upregulates expression of PTEN messenger RNA and protein, and leads to apoptosis. egr-1-/- cells, which cannot upregulate PTEN expression after irradiation, are resistant to ultraviolet-light-induced apoptosis. Therefore, Egr-1 can directly regulate PTEN, triggering the initial step in this apoptotic pathway. Loss of Egr-1 expression, which often occurs in human cancers, could deregulate the PTEN gene and contribute to the radiation resistance of some cancer cells.
391 citations
TL;DR: Nitroaromatic compounds on gold nanoparticles supported on ZrO2 can be reduced directly to the corresponding azo compounds when illuminated with visible light or ultraviolet light at 40 °C, and enables the selection of intermediates that are unstable in thermal reactions.
Abstract: Shedding light: Nitroaromatic compounds on gold nanoparticles (3 wt %) supported on ZrO2 can be reduced directly to the corresponding azo compounds when illuminated with visible light or ultraviolet light at 40 °C (see picture). The process occurs with high selectivity and at ambient temperature and pressure, and enables the selection of intermediates that are unstable in thermal reactions.
389 citations
TL;DR: Evidence suggests that early and perhaps later chemical reactions in photosynthesis may be partially reversible.
Abstract: 1. Green plants have been found to emit light of approximately the same color as their fluorescent light for several minutes following illumination. This light is about 10–3 the intensity of the fluorescent light, about one-tenth second after illumination below saturation or 10–6 of the intensity of the absorbed light.
2. The decay curve follows bimolecular kinetics at 6.5°C. and reaction order 1.6 at 28°C.
3. This light saturates as does photosynthesis at higher light intensities and in about the same intensity range as does photosynthesis.
4. An action spectrum for light emitted as a function of the wave length of exciting light has been determined. It parallels closely the photosynthetic action spectrum.
5. The intensity of light emission was studied as a function of temperature and found to be optimal at about 37°C. with an activation energy of approximately 19,500 calories. Two-temperature studies indicated that the energy may be trapped in the cold, but that temperatures characteristic for enzymatic reactions are necessary for light production.
6. Illumination after varying dark periods showed initial peaks of varying height depending on the preceding dark period.
7. 5 per cent CO2 reversibly depresses the amount of light emitted by about 30 per cent. About 3 minutes are required for this effect to reach completion at room temperatures.
8. Various inhibitors of photosynthesis were tested for their effect on luminescence and were all inhibitory at appropriate concentrations.
9. Irradiation with ultraviolet light (2537A) inhibits light production at about the same rate as it inhibits photosynthesis.
10. This evidence suggests that early and perhaps later chemical reactions in photosynthesis may be partially reversible.
388 citations
TL;DR: The question of the effect of pH on the inherent activity of the enzyme could not be solved until a water-soluble substrate could be found, and the spectrophotometric method described here is essentially a modification of the methods of Theorell et al. (8) and Tappel (7).
Abstract: Lipoxidase specifically catalyzes the oxidation of methylene-interrupted unsaturated fatty acids such as linoleic, linolenic, and arachidonic acids and their esters, to their res(pective peroxides (3). Various techniques have been devised for the determination of lipoxidase activity, including a colorimetric method based upon coupled oxidation, a manometric method, and spectrophotometric methods (6). The spectro,photometric method was developed after Holman and Burr (4) and Bergstr6m (1) independently observed an increase in ultraviolet light absorption, at 234 m>, when lipoxidase acted upon essential fatty acids. The increase in UV-peak absorption was then related to the amount of peroxide formation which was found to be proportional to time and to enzyme concentration (7, 8). According to Holman and Bergstrom (3), both the manometric and the coupled oxidation methods give aberrant indices of lipoxidase activity because of variations in the degree of dispersion of fatty substrates. The spectrophotometric method, on the other hand, does not have these disadvantages because it employs more homogeneous substrates. Although satisfactory results are obtained when the method is operated at pH 9.0 or above, where the unsaturated fatty acids are present in a solu;ble form, nevertheless, this nonphysiological pH presents a major disadvantage of the spectrophotometric method. It was therefore concluded by Holman and Bergstr6m (3) that the question of the effect of pH on the inherent activity of the enzyme could not be solved until a water-soluble substrate could be found. The method described here is essentially a modification of the methods of Theorell et al. (8) and Tappel (7). The polyunsaturated fatty acid is solubilized by the addition of a detergent, and with this soluble substrate the activities of purified and crude lipoxidase are demionstrated over a wide range of pH. Also, lipoxidase activities in germinating mung beans, over a period of 80 hours, are presented.
386 citations
TL;DR: Genetic variation in various sub-Saharan populations did not localize the origin of modern humans to a single geographic region within Africa; instead, it indicated a history of admixture and stratification, and illustrated the importance of African genomic diversity in understanding human evolutionary history.
Abstract: The history of click-speaking Khoe-San, and African populations in general, remains poorly understood. We genotyped ~2.3 million single-nucleotide polymorphisms in 220 southern Africans and found that the Khoe-San diverged from other populations ≥100,000 years ago, but population structure within the Khoe-San dated back to about 35,000 years ago. Genetic variation in various sub-Saharan populations did not localize the origin of modern humans to a single geographic region within Africa; instead, it indicated a history of admixture and stratification. We found evidence of adaptation targeting muscle function and immune response; potential adaptive introgression of protection from ultraviolet light; and selection predating modern human diversification, involving skeletal and neurological development. These new findings illustrate the importance of African genomic diversity in understanding human evolutionary history.
386 citations