ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07513.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.The dependence of primary photophysical and photochemical processes, especially of electron photoejection, in phenol and related compounds in aqueous solution on excitation intensity and excitation energy is examined. Theoretical and experimental evidence is presented for the possibility of three pathways for electron ejection: (1) A monophotonic pathway via the fluorescent state, which most probably does not involve the lowest triplet state; (2) a monophotonic pathway requiring higher excitation energies, which takes place in competition with internal conversion to the fluorescent state; and (3) a consecutive biphotonic pathway in which the lowest triplet state absorbs the second photon, and which can become predominant at high intensities, e.g. under flash conditions. It is shown that this model reconciles apparently conflicting results published in the literature.

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07514.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.Thermoluminescence excitation spectra of adenine, guanine, thymine and 1,3‐dimethyluracil were observed to be similar to their phosphorescence excitation spectra. Intensity dependence studies of thermoluminescence induced by ultraviolet light suggest that thermoluminescence could not be due to biphotonic ionisation of the molecule by UV. Evidence is presented which demonstrates that the fluorescence component observed in thermoluminescence of some compounds may not be due to triplet‐triplet fusion. Further, phosphorescence and thermoluminescence measurements following excitation with monochromatic light at very low intensities and short durations have shown for both a linear dependence on excitation intensity. It thus appears that direct entry of the electrons from the traps into the singlet manifold is necessary for explaining the fluorescence component of thermoluminesce

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07515.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.Wild‐type diploid yeast has been irradiated with visible light in the presence of eosin Y to investigate the photodynamic inactivation of this model eukaryote. Light, eosin Y and oxygen were all required for substantial inactivation, and no dark recovery was detected. Long periods of irradiation were required for greater than 90% inactivation, corresponding to a very small low‐dose quantum yield. Neither binding nor uptake of the dye by yeast was detected. Corrections for the photooxidative bleaching of eosin Y during irradiation indicate that bleaching causes a significant reduction in the apparent rate of inactivation. The results suggest that eosin Y acts as an extracellular sensitizer where the likelihood of damage to the cell envelope is enhan

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07516.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.Irradiation of isolated membranes ofSarcina lutea (Micrococcus luteus)with blue light rapidly inactivated the respiratory malate oxidase system under aerobic but not anaerobic conditions. This inactivation was much faster than that seen in whole cells suggesting that the intact organism possesses protective mechanisms capable of preventing or repairing light damage. Three photosensitive sites have been detected by comparing the effect of blue light on membranes from the carotenoid‐containing wild‐type and a carotenoidless mutant. The sites have been identified as the initial malate dehydrogenase enzyme, a flavoprotein assayed by phenazine methosulphate reduction, a sulphydryl group associated with the dehydrogenase complex but not involved in phenazine methosulphate reduction and the respiratory quinone, menaquinone. Menaquinone was found to be sensitive only in carotenoidless membranes and not in membranes from the pigmented wild‐type. Studies of the variation of photosensitivity with wavelength suggest that the three sites are sensitized by different chromophores and that the quinone acts as its own photosensi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07517.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.A pathogenic strain ofVibrio parahaemolyticus, strain WP1, is about 5 times more sensitive to killing by ultraviolet light than is the non‐pathogenic strain WP28, but WP1 cells have an efficient liquid‐holding recovery. The cellular DNA of both strains is fragmented shortly after ultraviolet irradiation, but the fragmented DNA is converted in a short time to the initial large molecular size in WP28 cells. In WP1 cells, however, the DNA molecules were degraded rapidly without any apparent rejoining in a growth condition. Post‐irradiation liquid‐holding made the DNA of WP1 cells stable, as supported by the recovery of DNA synthetic activity in thes

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07518.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.The spectral distribution of radiant energy on the floor of three typical English woodlands (birch, beech and oak) has been monitored throughout the whole growing season. The results are presented in terms of the changes in the ratio of the photon fluxes at 660 nm and 730 nm (τ) and in the photosynthetically active radiation (PAR). The results are discussed in relation to the hypothesis that the role of phytochrome is to detect changed light quality due to mutual shading and to direct development accordingly

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07519.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.The use of repair deficient strains of bacteria for detecting mutagenic properties of chemical species is now an established technique. In this paper we present inactivation results obtained withEscherichia coliK12 AB2480 (uvr A rec A) which indicate thatp‐aminobenzoic acid, a common component of sunscreening formulations, may increase the frequency of lethal damage induced in DNA when cell populations are exposed to near ultraviolet radiation.Preliminary experiments, utilising the selective action of photoenzymatic repair, indicated that the sensitisation to near ultraviolet radiation is partially but not wholly due to increased formation of pyrimidine dimer

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07520.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.Poliovirus when added to tapwater, sewage or seawater was readily photoinactivated by methylene blue and visible light. Typically, almost 2.5 logs of virus could be inactivated upon a 5‐min exposure to 670 nm light (20 W/m2) in solutions containing 13 μMmethylene blue at pH 10.0. A biphasic inactivation curve was produced for poliovirus, regardless of dye concentration, pH, temperature, sensitization time, nature of suspending solution or sequence of light exposure. These results indicated that a multi‐hit inactivation event was occurring. Preincubation of the dye‐virus mixture at 24°C increased the rate of virus photoinactivation. Dye concentrations above 26 μMhave little advantage in increasing the amount of virus photoinactivated. Significant inactivation of the virus in the dark occurred at high dye concentrations (5

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07521.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.In this work, the non‐tryptophan fluorescence (360 nm excited; 440 nm emitted) of human lens proteins was found to be intensified by exposing whole lens homogenates to near‐UV light in the presence of tryptophan photoproducts. The induced fluorescence accumulates mainly in the soluble phase proteins, whereas in aging and brown cataractous lenses, the major fluorescence is found in the insoluble proteins. Using SDS‐polyacrylamide gel electrophoresis with densitometric and fluorescence scanning techniques, the polypeptide chains of the three major protein fractions were analyzed for their specific non‐tryptophan fluorescences. The same chains were found in all fractions. Two chains (11,000 and 45,000 daltons) were found to accumulate most of the induced fluorescence. These also contained the greatest intrinsic fluorescence initially. The data indicates that specific polypeptide chains in the lens proteins are most sensitive to modifications due to their exposure to near‐UV light in the presence of tryptophan phot

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07522.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY