摘要:

Abstract—In an ethanolic solution native T7 DNA can undergo conformational transitions from the B conformation (0% ethanol) to the C‐like (60% w/w ethanol) and the A (80% w/w ethanol) conformations. We have investigated the formation of three classes of thymine‐derived photoproducts in T7 DNA irradiated (280 nm) in the B, C‐like, and A conformations, which were monitored by circular dichroism measurements. We find that the predominant class of thymine‐derived photoproducts in any conformational state is cyclobutyl dipyrimidines. While the ‘spore product,’ 5‐thyminyl‐5,6‐dihydrothymine, which belongs to another class of photoproductsf does form in native DNA in the A conformation, its yield in denatured DNA at 80% ethanol is the same as that in native DNA. The yield of pyrimidine adduct, a third photoproduct class, is a maximum at 50–60% ethanol. This effect of ethanol is probably not due to the ethanol‐induced C‐like conformation, however, since pyrimidine adduct formation is not enhanced when T7 DNA is irradiated in the C conformation in 6MCsCl or in intact phage. We conclude from these and other data in the literature that the degree of hydration rather than the conformational state is the critical factor in determining which of the photoproduct

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06867.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—When log phase cells of wild‐typeE. coliK‐12 were maintained in growth medium after X irradiation, they became progressively more resistant to a subsequent exposure to UV or X radiation. The time to achieve maximum resistance was about 60 min. TheuvrB, uvrD, polAand certainexrAstrains (W3110 background) also demonstrated this X ray‐induced resistance to subsequent UV or X irradiation butrecA, recB, lex(AB1157 or W3110 backgrounds) and otherexrAstrains (AB1157 background) did not. The resistance induced in wild‐type,uvrBanduvrDcells was characterized by the production or enhancement of a shoulder on the survival curves obtained for the second irradiation, while the resistance induced in the W3110exrAstrains was expressed only as a change in slope. The induction of resistance in the W3110exrAstrain was not inhibited by the presence of chloramphenicol, but that in the wild‐type cells appeared to be. The production or enhancement of a shoulder on the survival curves of therec+lex+exr+cells is consistent with the concept of the radiation induction of repair enzymes. Alternative explanations, however, ar

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06868.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—Bilirubin has been found to sensitize the photodynamic inactivation of several enzymes in the isolated membrane (ghost) of the human red cell. When ghosts (pH 8.0, 10°C) + bilirubin (0.1 mM) were irradiated with blue light (350 Wm‐2), the activity of glyceraldehyde 3‐phosphate dehydrogenase decayed witht1/2≃ 15 min. No effect was observed in the absence of pigment or with incident yellow light. Diazabicyclo‐octane (DABCO) sharply reduced the inactivation rate, suggesting that1O2is involved. Sodium dodecyl sulfate‐gel electrophoresis of ghosts containing fully inactivated glyceraldehyde 3‐phosphate dehydrogenase revealed no change in the polypeptide band corresponding to the subunit of the enzyme. Solubilized enzyme, which was similarly photosensitive, could be partially protected by nicotinamide adenine dinucleotide or glyceraldehyde 3‐phosphate. The integral enzymes Mg2+‐ATPase, Na+, K+‐ATPase, and acetylcholinesterase were also affected. Under the above conditions and bilirubin = 0.37 mM, these enzymes were photoinactivated in first‐order fashion,k≃ 2, 1.2 and 0.2 h‐1, respectively. The rate of decay of total ATPase was found to vary as the square root of the bilirubin concentration over the range 7–370 μM. At a fixed bilirubin concentration (0.37 mM), this rate was also shown to be directly proportional to light intensity. Inasmuch as the —SH content of bilirubin‐containing ghosts diminished during irradiation, oxidation of essential cysteine residues could be responsible for the inactivati

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06869.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—DNA single‐strand breaks were produced inuvrAanduvrBstrains ofE. coliK‐12 after UV (254 nm) irradiation. These breaks appear to be produced both directly by photochemical events, and by a temperature‐dependent process. Cyclobutane‐type pyrimidine dimers are probably not the photoproducts that lead to the temperature‐dependent breaks, since photoreactivation had no detectable effect on the final yield of breaks. The DNA strand breaks appear to be repairable by a process that requires DNA polymerase I and polynucleotide ligase, but not therecA, recB, recF, lexA101 oruvrDgene products. We hypothesize that these temperature‐dependent breaks occur either as a result of breakdown of a thermolabile photoproduct, or as the initial endonucleolytic event of auvrA,uvrB‐independent excision repair process that acts on a UV photoproduct other than the cyclobutane‐type

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06870.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—A mid‐UV dosimeter has been developed based on the irreversible photochemical conversion of 3′‐[p‐(dimethylamino)‐phenyl] spiro‐[fluorene–9,4′‐oxazolidine]–2′,5′‐dione (1) top‐dimethylamino‐N‐fluoren‐9‐ylidine aniline (2), carbon monoxide and carbon dioxide. Formulations of1in a polycarbonate film matrix are colorless, thermally stable, and undergo photolysis only when exposed to wavelengths of less than 350 nm. The red photoproduct2is both thermally and photochemically stable under dosimeter use conditions. The depth of red color developed depends solely on the degree of exposure to mid‐UV radiation. In outdoor studies color intensity steadily developed during an initial 2 h of exposure to noontime Miami June sunshine. Color comparators representing consecutive 15–20 min exposure increments of this sunshine were readily distinguishable from each other by visual inspection. The comparators could be visually matched to colors generated by the dosimeter film formulation, and covered the exposure range of interest for avoidance of sunburn. This photochemical mid‐UV dosimeter is seen to fulfill all the re

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06871.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—The porphyrinogenic drug, 3,5‐diethoxycarbonyl 1,4‐dihydrocollidine (DDC) when administered orally to rats evoked large increases in hepatic δ‐aminolevulinic acid synthetase (ALAS) activity and hepatic protoporphyrin levels. These increases varied markedly according to light exposure patterns of the animals. DDC‐treated animals continuously exposed for one week to fluorescent Blacklight lamps (Westinghouse FS‐40) demonstrated a greater than two‐fold increase in hepatic ALAS and a greater than threefold increase in liver protoporphyrin levels as compared to DDC‐treated animals exposed to ambient light‐dark cycling. Furthermore, the skin of porphyric animals continuously exposed to light showed larger increases in porphyrin content as compared to rats exposed to ambient light. These studies indicate that light exposure patterns can profoundly alter the activity of the hepatic heme pathway in the rat and suggest that light exposure could play a role in the production of drug‐indu

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06872.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—The small amounts of chlorophyll precursors in dark‐grown cells ofEuglena gracilisKlebs var.bacillarisPringsheim and the presence of contaminants which interfere with their purification have made their isolation and characterization difficult. We now extract cells with acetone: 0.1 M NH4OH (9:1 v/v). Protochlorophyll is obtained by extracting this solution with petroleum ether (30–50° b.p.) and extracting this petroleum ether fraction with 80% acetone to remove substances which interfere with subsequent chromatography. Protochlorophyllide remaining in the original acetone: NH4OH fraction is extractable into diethyl ether after adjusting the pH to approximately 5.5. Both pigments are verified and further purified by chromatography on Whatmann 3 MM paper using benzene:petroleum ether:acetone (30:10:1) or cellulose MN 300 thin layers with methanol:methylene chloride:water (100:18:20). These pigments resemble their well‐described barley counterparts in solubility properties, spectral absorption maxima in ether (432, 530, 571 and 623 nm) and chromatographic behavior. Substantial amounts of protopheophytin and protopheophoribide are also found along with the Mg2+— containing pigments in cell extracts even when precautions are taken to avoid loss of Mg2+during extractions and purification.Using heated cells before and chilled solvents after illumination to preclude enzymatic modification of pigments, chlorophyll and very small amounts of chlorophyllide are found as products of the photo‐conversion of the protopigments suggesting that both protochlorophyll and, to a much smaller extent, protochlorophyllide are photoconvertible in these organisms. These properties join several others which suggest that theEuglenachorophyll‐forming system more closely resembles that found in young bean leaves rather than the chlorophyll‐forming system of the older leaf material

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06873.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—The irradiance and wavelength dependence of phytochrome destructionin vivowas analysed in etiolated cotyledons ofCucurbita pepoL. and etiolated seedlings ofAmaranthus caudatusL. In contrast to grass seedlings, the rate ofPtotdestruction could only be saturated by light sources that establish relatively highPfrlevels (about 50% of total phytochrome, corresponding to the photostationary state established by 693 nm light). To explain the irradiance dependence ofPtotdestruction in dicots at irradiances above 0.1 Wm‐2, where the light reaction is at least one order of magnitude faster thanPfrdestruction, we suggest there is a fast intercalary dark reaction between photoreaction and destruction. This dark reaction is probably—as in grass seedlings—the binding ofPfrto a receptor site. We conclude that the differences between dicots and grass seedlings with respect to the phytochrome system are of a quantitative rather than a qualitative

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06874.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—The interaction of ionizing radiation and UV‐light regarding colony forming ability in 3 diploid yeast strains ofSaccharomyces cerevisiaewas investigated. A wild type and two radiation sensitive mutants were used. No difference in the response of the three strains could be detected when the UV dose was given first, but when ionizing radiation was applied shortly before UV, there were essential differences depending on the kind of mutation. The involvement of repair mechanisms in the interaction is discus

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06875.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—Enzymes can provide well defined functional targets for determining the availability and reaction characteristics of light sensitive probes. Trypsin and chymotrypsin are inhibited by flash photolysis with a photoprobe, 4‐fluoro‐3‐nitrophenylazide (FNPA). Inhibition is competitive in the dark, and non‐competitive (irreversible) following photolysis of the FNPA enzyme solution. Photoinactivation is dependent upon the concentration of FNPA, the flash rate, and the time of photolysis. The enzymes can be protected from photolytic inactivation with FNPA if photolysis is carried out in the presence of 2,4‐dinitrophenol or 4‐fluoro‐3‐nitroaniline which compete with FNPA for binding sites. The photo‐probe is effective over a wide pH range (i.e. pH 2–11), and provides a sensitive tool for probing conformational and charge adjustments which increase or decrease the affinity of the binding site. Chymotrypsinogen was also sensitive to photolysis, indicating that FNPA binding sites are present in

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06876.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY