摘要:

Abstract—Several high energy ketone triplet sensitizers, e.g. carvone, camphor, 3‐methylcyclohexanone, benzoin and 3‐methylindanone, were studied as photosensitizers for the splitting of dimethylthymine dimers. The absence of splitting in all cases and the lack of quenching of benzoin and 3‐methylindanone triplets by thetrans‐antidimer of dimethylthymine strongly suggests that cleavage of dimethylthymine dimers cannot be achieved by a triplet mechanism on irradiation at Λ>300 nm. The absence of optical rotation in the recovered chiralcis‐antidimethylthymine dimer after sensitized photolysis (12% splitting) in the presence of (—)‐tryptophan suggests that. in highly polar solvents, such as methanol, where reaction probably takes place according to an electron transfer mechanism involving ion‐pair intermediates, close approach of the sensitizer and substrate does not occur. To the extent that these results can be extrapolated to sensitized cleavage ofcis‐synpyrimidine dimers in DNA brought about by action of photoreactivating enzyme or conventional photosensitizers, a mechanism involving dimer triplet states app

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb06905.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—In 1, 1, 2‐trichlorotrifluoroethane solution biliverdin physically quenches singlet oxygen at a rate of 8 × l0sM‐1s‐1and reacts chemically at 6 × 105M‐1s‐1to give a red product. In D, O solution the rate constants are PD dependent and range from 1.5–6 times 1010M‐1s‐1for quenching and the chemical rate varies from 3–5 × 108M‐1s‐1

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb06906.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—Datura stramoniumL. is a local lesion host for TMV‐RNA and DNA‐containing cauliflower mosaic virus (CAMV).Daturacan photorepair UV‐damaged TMV‐RNA and CAMV, giving photoreac‐tivation sectors of 0.40 and 0.33, respectively. Dose response curves for photoreactivation of TMV‐RNA and CAMV show that 4540 min of cool white light (15 W.m‐2) is required for maximum photoreactivation. Blue light and near UV are equally effective in photoreactivating UV‐irradiated TMV‐RNA, whereas near UV is initially more effective than blue light for the photorepair of UV‐inactivated CAMV. Higher doses of near UV apparently inactivate the CAMV photorepair system. In the case of CAMV, photoreactivating light must be applied immediately after inoculation with the virus. Two to three hours of incubation in the dark after inoculation results in complete loss of response to photoreactivating irradiation. In contrast, limited photoreactivation of TMV‐RNA occurs even after 4 h of dark incubation after inoculation, although photoreactivating irradiation is most effective when applied immediately after inoculation. Light is required for the maintenance of photoreactivation for both TMV‐RNA and CAMV.Daturasplaced in the dark for six days lose their ability to photoreacti‐vate. Recovery of the TMV‐RNA photorepair system is rapid; complete recovery attained with 90 or more min of white light (15 W m‐'). Recovery of CAMV photorepair system is slow; 90% recovery attained after only 20 h of light. However, full recovery can be induced by as little as 6h of light when CAMV is inoculated 24 h after the onset of illumination. These results suggest two photorepa

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb06907.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—An attempt was performed to estimate survival and course of DNA synthesis inEscherichia coliB/rhcr'andhcr‐cells in relation to the amount of unexcised dimers.In exponential growinghcr+cells irradiated with 30 Jm‐2, dimers were almost completely excised and survival of cells was equal to about 3%. In thehcr+cells prestarved for amino acid and thymine and irradiated by the same fluence, survival of cells was almost equal while two thirds of dimers remained unexcised and could be detected in the hybrid DNA consisting of parental and daughter chains. In exponentially growinghcr+‐cells irradiated with 20Jm‐, the same amount of dimers was produced which remained unexcised in the prestarvedhcr+cells. However, their survival was equal to about 0.02%.Despite the great differences in dimer contents, about one third of DNA was replicated after UV in both exponentially growing and prestarvedhcr+cells producing well defined HL‐hybrid peak, and the newly synthesized DNA was normal‐sized. Inhcr+cells which contained approximately the same amount of dimers as inhcr+prestarved cells, the amount of replicated DNA was too low to form a detectable density labelled hybrid peak, and the newly synthesized DNA was in short pieces.Thus, whenhcr+andhcr+‐cells contain the same number of residual dimers, they have different levels of tolerance

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb06908.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—The photomediated induction of interstrand cross‐links by 8‐methoxypsoralen has been measured in the epidermal DNA of hairless mice. Equivalent efficiencies for cross‐link induction were determined for HRS/J/Anl and SKH: hairless‐1 mice. A wavelength dependence on the relative efficiency of cross‐link induction was observed; a broad spectrum light source, 300–400 nm, was approximately 5 times more effective in cross‐link formation than a 365 nm light source. Repeated exposure to 8‐methoxypsoralen followed by ultraviolet light, 5 times a week for 6 weeks, altered epidermal thickness and resulted in a decreased efficiency for DNA cro

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb06909.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—The photosensitizing effects of 8‐methoxypsoralen on the skin of two strains of hairless mice were studied using fractionated exposure to UV Spectral dependent differences for tumorigenesis were studied by comparing the tumor responses to three different spectra; the exposure levels for each spectrum here adjusted in proportion to their relative efficiencies for tissue damage and cytokinetic responses. There were no strain differences in the spectral dependent induction of cutaneous damage or estimates of the photomediated interstrand cross‐linking of epidermal DNA by 8‐methoxypsoralen.Squamous cell carcinomas were induced in the photosensitized skin of both strains of mice after fractionated exposures to emissions at principally 365 nm. Exposures to a broader spectrum of light resulted in the earlier appearance of tumors in the photosensitized skin of the SKH: hairless‐1 mice, but produced few or no tumors in the HRS/J/Anl strain. In a second series of experiments;mice were exposed to a fluorescent sun lamp prior to each combined treatment of psoralen and exposure at 365 nm to determine the influence of shorter wavelengths of UV on the tumor response. These treatments resulted in an enhanced expression of tumors in the SKH:hairless‐1 mice as compared to the HRS/J/Anl strain.Under the conditions of the experiments, the marked strain and spectral dependent differences for tumorigenesis demonstrated that although treatments that induce psoralen photoadducts also induce tumors. there was no apparent quantitative correlation between the occurrence of DNA cross‐links and the incidence of tumors. The results also suggested, first, an interaction between UV (280–400 nm) induced photoproducts and psoralen photoadducts and secondly, a strain difference in the oncogenic effects of t

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb06910.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—Retinylidine Schiff base spectra have been investigated in a variety of solvents that were chosen primarily to mimic possible environments of the chromophore in visual pigments. These studies have identified particular amino acid side chains which can have important influences on visual pigment spectra. Most amino acid side chain analogues or solvents which mimic the peptide bond environment have little effect on retinylidine Schiff base spectra. Tyrosine, tryptophan, and cysteine analogues and ionized aspartic and glutamic acid analogues produce pronounced red shifts in the spectra. As is explained in more detail in the following paper the presence of these amino acids in the chromophore “pocket” of the protein is sufficient to account for the spectra of many visual pigments. Calculations of the spectra of protonated Schiff bases under a variety of conditions have been considered in conjunction with the spectral data to provide a model for the nature of the chromophore interactions with its environment.In solution and in rhodopsin the protonated Schiff base linkage is likely to be associated with an anion. The presence of certain amino acid side chains along the remainder of the retinal chain in the protein can modify the spectrum by altering the polarizability and polarity of the environment. The polarity in the region of the ionone ring appears to be particularly important for shifting the spectrum. In solution the nucleophilicity of the solvent also has an important influence on the anion‐protonated Schiff base region of the chro

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb06911.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—Electronic absorption spectra of retinal (A,) and 3‐dehydroretinal (A2) Schiff bases have been studied under a variety of solvent conditions. The spectra of the two species have different solvent dependencies. Variation in solvent conditions have a larger effect in the A2spectra, although the wavelength maxima of A, and A, Schiff bases smoothly converge in solvents that shift them both to shorter wavelengths. Convergence curves for the A, and A2Schiff bases can thus be generated in solution which resemble the convergence curves observed in visual pigments. It is also shown that the spectra of visual pigments made by combining A, and A2with opsins from various fish species can be reproduced theoretically by changing the number of tryptophan or tyrosine side chains which are assumed to line the chromophore pocket. Discrete changes in the number of these side chains can exactly reproduce the clustering effect observed for a large variety of fish visual pigments. Variations in solvent characteristics which are analogous to possible chromophore environments in visual pigments have thus been shown to effect Schiff base spectra in such a way as to mimic the bathochromic shift, spectral convergence, and spectral clustering phenomena exhibited by visual pigme

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb06912.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—The oxygen yield per flash ofChlorellain the presence of redox components such as benzo‐quinone, hydroquinone, Fe(CN)B‐and IrC12‐‐ has been studied in an atmosphere of 10ppm 02. When oxidants are added to the cells, the familiar Joliot‐Kok oscillations with maximum yield on the third flash and periodicity four are observed. As hydroquinone is progressively added, the oscillations fade out and the steady state decreases. The pattern of O2evolution approaches a monotonic climb to the steady state with no obvious oscillatory behavior. A novel method for analyzing this data has been developed. A simple fourth order linear difference equation with constant coefficients is presented. This equation is capable of describing the systematic transition from oscillatory to monoto

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb06913.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—Various nitrogen containing compounds have previously been shown to quench singlet oxygen (10z). When measuring the dimol1O2light emission arising from the H2O2/OCI‐ reaction, we found that certain cyclic diamines increase the emission of light, while other amines were inhibitory. This increase of light emission was seen with both 1, 4diazabicyclo[2.2.2]octane and N, N'‐dimethylpi‐perazine but not with acyclic analogues. Sodium azide inhibited both the normal and enhanced light emission. The enhanced light emission shows spectral properties characteristic oflO2dimol e

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb06914.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY