摘要:

AbstractThe formation of a compound I type ferryl complex in the reaction of methemoglobin (MetHb) and metmyoglobin (MetMyo) with hydrogen peroxide is accompanied by strong chemiluminescence. An approach to identify the nature of the light‐emitting species was made by the use of quenchers and sensitizers reacting with singlet oxygen and compounds interfering in the formation and reactivity of other reactive oxygen species.Singlet oxygen is not the source of light emission. This could be concluded from the results obtained using the specific singlet oxygen trap 9,10‐anthracenedipropionic acid (ADPA) in combination with high‐performance liquid chromatography (HPLC) analysis. The singlet oxygen adduct of ADPA was not formed in the incubation systems (MetHb or MetMyo/H2O2). Instead, ADPA was oxidized by the ferryl ion to a different oxidation product, which was characterized by HPLC and IR spectroscopy. In the case of MetHb‐related chemiluminescence, light emission does not result from a single source. Both, SH‐groups and O2.¯radicals are involved because blocking of thiol‐groups with N‐ethylmaleimide (NEM) and scavenging of O2.¯(by superoxide dismutase) suppressed chemiluminescence by 50% and 30%, respectively. Development of MetMyo‐related chemiluminescence is not dependent on thiol groups (which are not present in the globin moiety) and also 02.¯is not involved. Although generation of chemiluminescence in MetHb and MetMyo seems to follow different mechanisms, both types of light‐emitting species are sensitive to antioxidants, such as uric acid and ascorbate. The detection of the respective free radicals by means of ESR demonstrates that both MetHb‐ and MetMyo‐mediated chemiluminescence is associated with a strong one‐electron oxidizing species, which seems to be identical with the light‐emitting source itself. Also desferal, which was originally used to exclude the involvement of a Fenton‐type reaction, was readily oxidized to the nitroxide free radical associated with a strong decrease of chemiluminescence. This quenching effect was not dependent on iron complexation because the addition of iron was ineffective. In summary, chemiluminescence is not restricted to a single chemical process but is related to different one‐electron transfer reactions from globin

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05072.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractIrradiation of ketoprofen in neutral aqueous medium gave rise to 3‐ethylbenzophenone as the major photoproduct. Its formation is justifiedviaprotonation of a benzylic carbanion or hydrogen abstraction by a benzylic radical. Minor amounts of eight additional compounds were isolated. Four of them are derived from the benzylic radical: 3‐(1‐hydroperoxyethyl)benzophenone, 3‐(1‐hydroxyethyl)benzophenone, 3‐acetylbenzophenone and2,3‐bis‐(3‐benzoylphenyl)butane. The other four products involve initial hydrogen abstraction by the excited benzophenone chromophore of ketoprofen: 1,2‐bis‐(3‐ethylphenyl)‐1,2‐diphenyl‐1,2‐ethanediol, 2‐(3‐benzoylphenyl)‐1‐(3‐ethylphenyl)‐1 ‐phenylpropan‐1 ‐01,α ‐(3‐ethylphenyl)phenylmethanol, 1,2‐bis‐[3‐(2‐hydroxycarbonylethyl)phenyl]‐1,2‐di‐phenyl‐1,2‐ethanediol. The latter process was found to mediate the photoperoxidation of linoleic acid through a type I mechanism, as evidenced by the inhibition produced by the radical scavengers butylated hydroxyanisole and reduced glutathione. The major photoproduct, which contains the benzophenone moiety but lacks the propionic acid side chain, also photosensitized linoleic acid peroxidation. Because lipid peroxidation is indicative of cell membrane lysis, the above findings are

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05073.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractBenzophenone‐mediated photosensitization of 2′‐deoxyguanosine and its 3′,5′‐di‐O‐acetyl derivative, used as DNA model compounds, in oxygen‐saturated water‐methanol (1:1) solution results in the nucleophilic addition of methanol to the guanine base. The resulting modified nucleosides have been isolated by reverse‐phase high‐performance liquid chromatography and characterized by extensive spectroscopic measurements including13C andIH nuclear magnetic resonance, fast atom bombardment mass spectrometry and circular dichroism as the 2R and 2s diastereoisomers of 1‐(2‐deoxy‐˜‐o‐erythro‐pentofuranosyl)‐2‐methoxy‐4,5‐imidazolinedione and their related 3′,5′‐di‐O‐acetyl derivates. Information concerning the absolute configuration of the two pairs of diastereoisomers was inferred from detailed nuclear Overhauser effect experiments. A reaction mechanism, involving guanine radical intermediates, is proposed to exp

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05074.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractSensitivity of plants to UV‐B radiation (280–315 nm) is often reduced at high background irradiance. Interpretation of plant responses to potential increases in solar UV‐B requires improved understanding of interactions between UV‐B and other environmental parameters. In this study, photosynthetically active radiation (PAR, 400–700 nm) was kept approximately constant (38 mol m‐2per day) while the daily blue light fluence (BL, 400–500 nm) was varied between 0.23 and 2.68 molm‐2. Two lines of cucumber (cvs Ashley and Poinsett) with differential sensitivity to UV‐B were compared. At low BL, 3 days of UV‐B treatment (21 kJ m‐2biologically effective radiation per 10 h per day) caused severe inhibition of growth in a developing leaf in both cultivars. Growth effects were detectable sooner and were accompanied by chlorotic lesions in the sensitive cultivar (cv Poinsett). Supplemental BL progressively reduced symptoms, consistent with an important role for BL photoreceptor(s) in prevention or repair of UV‐B damage. Ultraviolet‐induced increases in UV‐absorbing compounds on an area basiswere significant within 24 h of the start of the treatment but were independent of BL fluence over the range tested, suggesting that bulk accumulation of screening pigments did not contribute to BL‐dependent amelioration of UV damage. However, BL did stimulate net increases in extractable UV‐absorbing compounds on atotal leaf busis, while high‐performance liquid chromatography analysis indicated that BL and UV‐B acted synergistically to increase specific components. Thus, the data do not necessarily exclude UV‐absorbing compounds from an important role in overall UV‐B protection nor do they rule out some more specific function for these compounds (e.g. antioxidants). Finally, BL effects on UV‐B alteration of leaf growth and accumulation of UV‐absorbing compounds were not saturated under the conditions used here, suggesting that BL may contribute to interactions between UV‐B and natural levels of background irradiance. Caution is urged in the interpretation of data on UV‐B effects

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05075.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractSpecific leaf weight (SLW), the ratio of leaf dry matter to area, often increases in plants exposed to elevated UV‐B radiation (280–315 nm). Increased SLW can result from greater leaf thickness or increased leaf density (e.g. accumulation of high density substances in cells). The basis for large increases in SLW was examined in the first and third leaves of cucumber differing in developmental stage at the start of UV treatment. Leaf 1 was approximately 50% fully expanded, while leaf 3 had just unfolded. It is shown here that up to 80% of the UV‐generated change in SLW in leaf 1 was caused by accumulation of nonstructural carbohydrates, especially starch (increasing from 13 to 23% of total dry weight). Leaf 3 contained a much smaller proportion of nonstructural carbohydrates (less than 8%) and the effect on SLW was correspondingly less. As shown in the previous paper, UV‐B inhibition of growth in leaf 3 was reversed by supplemental blue light (BL) in a fluence‐dependent manner between 0.23 to 2.68 mol m2perday. Fluence‐response curves revealed that supplemental BL reversed both the UV‐induced accumulation of starch and increase in SLW in leaf 1 over the same range. The data are consistent with a back‐up of photosynthate into leaf 1 as a result of UV‐B inhibition of growth in leaf 3. The data also demonstrate that increases in SLW cannot be assumed to represent increases

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05076.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractGoldfish cells (RBCF‐1) cultured at different cell densities were harvested and their photorepair (PR) abilities were examined in terms of survival. Photorepair ability gradually increased during the phase of logarithmic growth, reaching a maximum in cells at the confluent state. This enhancement of PR ability disappeared 12 h after replating of cells in fresh medium. A number of growth‐inhibiting treatments (serum depletion, UVC, hydroxyurea [HU], change in incubation temperature) were tested for their ability to induce PR. The treatment of cells with HU and serum depletion induced PR while the other treatments did not. The increase in the ability to perform PR after treatment with HU or serum depletion returned to normal levels more rapidly than that after fluorescent light treatm

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05077.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractAphr‐genefrom the filamentous fungusNeurosporu crassawas overexpressed inEscherichia colicells, yielding a biologically active photolyase. After purification till apparent homogeneity, the 66 kDa protein was found to contain equimolar amounts of 5,1O‐methenyltetrahydrofolic acid (MTHF) and FAD, classifying it as an MTHF‐type photolyase. Compared to other MTHF photolyases the absorption maximumof Neurosporuphotolyase is shifted fromca380 nm to 391 nm (t = 34 800), while an additional shoulder is present at 465 nm. In dark‐adapted enzyme the FAD chromophore is predominantly present in the oxidized form, in contrast withE. coliandSaccharomyces cerevisiuephotolyase, which contain mainly semiquinone or fully reduced FAD, respectively. Preillumination or dithionite treatment converted oxidized FAD inNeurosporaphotolyase into the fully reduced form, with a concomitant shift of the absorption maximum from 391 to 396 nm and disappearance of the 465 nm shoulder. The action spectrum of photoreactivation coincides with the absorption spectrum of preilluminated (reduced) photolyase, extending the spectral region of MTHF‐type photolyases from 380 till 396 nm. A quantum yield of 0.57 was obtained for the overall repair reaction. Comparison of spectral properties of FAD inNeurosporaphotolyase and the model compound lumiflavin points to an apolar microenvironment of photolyase‐bound FAD.Neurosporuphotolyase has distinct advantages overE. coliphotolyase as it is more stable and contains a full complement of c

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05078.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe effects of ultraviolet C (UVC) irradiation on nucleosome assembly and its stability were investigated quantitatively using anin vitronucleosome assembly system comprising a plasmid DNA of pBR322 and core histones isolated from rat ascites hepatoma cells. Nucleosomal formation was estimated by analyzing the resulting DNA supercoils. When UVC‐irradiated (3000 J/m2) DNA was used as a substrate for the nucleosome assembly system, the nucleosomal formation efficiency was reduced by half compared with nonirradiated DNA. On the other hand, when the reconstituted nucleosomes (minichromosomes) on the nonirradiated DNA were irradiated with UVC (3000 J/m2), about half each were disrupted and retained. These results indicate that it is difficult for UV‐damaged DNA regions to supercoil around the histone octamers to form nucleosomes and that the histone octamers in the UV‐damaged nucleosomes tend to be dissociated fro

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05079.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe crystal and molecular structure of the title compound 4 have been determined by single crystal X‐ray crystallography. The structure shows the typical S,‐ruffled conformation observed for Ni(II) tetrapyrroles. Compared to the structure of the methyl ester of (132‐demethoxycarbonyl‐pheophorbidato a)nickel(II), 4 shows a smaller Ca‐Cm‐Cmangle and a higher degree of conformational distortion at the methyl‐substituted C20 position. This local distortion of the macrocycle might account for the bathochromic shifted absorption spectra of the bacteriochlorophyllsccompared to the d‐series. Crystal data: C35H38N4NiO3; tetragonal, P43212, a = 15.335(7) Å, c = 25.11(2) Å, V = 5904, Z = 8, λ(Mo Kα) = 0.71069 Å, μ= 0.701 mm−1, P(000) = 2624, 130 K, R = 0.058 for 5700 ref

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05080.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe mechanism of photocytotoxicity mediated by a lysosomotropic photosensitizer, Nile blue derivative (NBS‐61), in relation to lysosome destruction was examined by lowering the intracellular pH with low extracellular pH and an ionophore, nigericin. The treatment performed after photoirradiation had minimal effect on the cytotoxicity. However, when the treatment was initiated before photoirradiation, it caused a three orders of magnitude enhancement on cytotoxicity with a two orders of magnitude enhancement by nigericin alone. This effect on cytotoxicity resembles closely that observed on photosensitization mediated by chloroaluminum phthalocyanine. The enhancement in this case has been attributed to the synergistic interaction between photodamage and perturbation of ion transports across mitochondrial or plasma membranes by nigericin. Because these are not the main sites of localization for Nile blue photosensitizers nor their initial targets of photocytotoxic action, data from the present study suggest the possibility of an intracellular dye translocation induced by nigericin, which redistributes the Nile blue photosensitizer from lysosomes to other sites, as a possible cause of the enhancement of cytotoxicit

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05081.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY