摘要:

Abstract—Structural alterations of DNA irradiated with UV light were analyzed by the agarose gel technique. Relaxed, circular pAT 153 DNA molecules were sensitized by broad band radiation with a maximum at 313 nm in the presence of silver ions or irradiated with 254 nm light in buffer only. In both cases the electrophoretic mobility of DNA topoisomers was altered as a linear function of UV exposure. For DNA irradiated in the sensitized reaction the unwinding angle per site sensitive toMicrococcus luteuspyrimidine dimer endonuclease was found tobe–11.4°. This value is significantly smaller thanthe–14.3° already known for DNA topoisomers irradiated with 254 nm light. The irradiated DNAs were a very good substrate for theEscherichia coliphotoreactivating enzyme (PRE). However, the photoenzymic removal of all sites sensitive to the endonuclease specific for pyrimidine dimers was not coupled to a full restoration of the original electrophoretic mobility. Thirty and 23% of the unwinding were still present in the photoreactivated topoisomers and the unwinding angles per pyrimidine dimer were then recalculatedas–10.1°and–8.7° for DNAs irradiated with 254 nm and sensitized, respectively. The limited difference between these two values could result from the different base composition of the pyrimidine dimers generated in the conditions of irradiation used. These results show that the tertiary structure of DNA is measureably altered by UV photodamages other than pyri

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb02670.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—The photoreaction of 8‐methoxypsoralen (8‐MOP) with thymidine in solid film state yielded two 4′, 5′‐monoadducts (a pair of diastereomers) and three 3,4‐monoadducts. The stereochemistry of two 4′, 5′‐monoadducts was found to becis‐synandtrans‐synand one 3,4‐monoadduct wascis‐anti.In addition to these monoadducts, 3,4‐, 4′, 5′‐biadducts were also formed during the reaction, but the isolation of each isomer of these adducts was not successful; however, the formation of these biadducts was confirmed by UV, IR,

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb02671.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—The conventional flash photolysis of 1‐methylindole in aqueous media was studied at Λexcitation≥290 nm. The transients observed 20 μs after excitation consisted mainly of the radical cation (R+). the hydrated electron (e‐aq) and the triplet state (T). Electron counting experiments indicate that photoionization is the only source of R+with e‐aq/R+= 1.07±0.09 in neutral media. Quenching of the R+yield with H+indicates that the fluorescent state is the precursor to 80% of the photoionization events with the remainder probably arising from a prefluorescent state. The triplet decays with a lifetime of 29 μs in deaerated neutral media. This decay is unchanged by N2O saturation, but T reacts with acrylamide withk≥2.8 × 109M‐1. In 2MBr‐, R+and T yields are increased by factors of 2–3. Consideration of fluorescence quenching and T enhancement by Br‐permits an estimate of φIscbetween 0.33 and 0.49. The increased R+yield at high Br‐concentrations cannot be accounted for by induced photoionization

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb02672.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Benoxaprofen [2‐(4‐chlorophenyl)‐α‐methyl‐5‐benzoxazole acetic acid] is an anti‐inflammatory drug that causes acute phototoxicity in many patients. Photolysis studies in organic solvents (ethanol, benzene, dimethylsulfoxide) showed that benoxaprofen underwent both Type I and Type II reactions. Irradiation of an anerobic solution of benoxaprofen in ethanol resulted in hydrogen abstraction from the solvent to yield hydroxyethyl and ethoxyl radicals. In the presence of oxygen, superoxide, singlet oxygen and hydroxyethyl radicals were detected. Photolysis of benoxaprofen in air‐saturated benzene or dimethylsulfoxide gave superoxide. However, under anerobic conditions the drug yielded a carbon‐centered radical in benzene that could not be identified. These findings suggest that both oxygen‐dependent and oxygen‐independent processes may be important in the phototoxic r

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb02673.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Optical properties of the human brain in the wave‐length region from blue to near infrared are presented. There are significant variations in the optical penetration depth from the neonatal and to the adult brain. Typical values for the penetration depth in the adult brain are: 0.5 mm for blue/green, 1.5 mm for red and 3.5 mm for near infrared. The values for the neonatal brain are typically 2–3 times l

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb02674.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Ultraviolet (UV)‐irradiatedEscherichia coliK–12uvrAcells showed higher survival if plated on minimal growth medium rather than on rich growth medium, i.e., they showed minimal medium recovery (MMR). A 2‐hour treatment of UV‐irradiated cells with rifampicin inhibited the subsequent expression of MMR, and produced a large reduction in survival. We have recently isolated a new mutant (mmrA1) that does not show MMR. ThemmrAmutation protected UV‐irradiateduvrAcells from the effect of rich growth medium on survival, but not from the effect of rifampicin on survival. DNA daughter‐strand gap (DSG) repair in UV‐irradiated (4 J/m2)uvrAcells was inhibited to the same degree whether rich growth medium was added immediately after irradiation or after 10 min of postirradiation incubation in minimal growth medium. However, chloramphenicol added immediately after irradiation greatly reduced this repair; there was less reduction if it was added 10 min after UV irradiation. These findings suggest that MMR is an inducible repair phenomenon, and that rich growth medium inhibits this repair process itself rather tha

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb02675.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Salmonella typhimuriumstrains withsupXmutations are known to be sensitive to ultraviolet (254 nm) irradiation (UV) and to be protected by plasmid pKM101. Wild type (supX+) cells shut off their respiration after UV and are protected against their shutoff by pKM101. Respiration and survival studies were carried out on severalsupX strains with different genetic backgrounds. ThesupX strains shut off their respiration after low fluences of UV. Plasmid pKM101 protected asupX 83 (nonsense mutation) strain against respiration shutoff and killing but did not protect asupX35 (deletion mutation) strain against respiration shutoff or killing. When each of the twosupX genes were in the genetic backgrounds of the other, however, full protection was provided by pKM101. ThesupX35 strain not protected by pKM101 may have accummulated a modifying mutation. ThesupX locus is identical with one specifying topoisomerase I which removes negative superhelical turns from DNA. In the absence of this enzyme transcription of the DNA is increased. It is proposed that the exaggerated shutoff of respiration and increased killing ofsupX cells occurs because of the greater ease of transcription of an operon involved in UV‐induced respiration shut

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb02676.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Longwave UV irradiation of a frozen aqueous solution of khellin and thymine resulted in the formation of a 2+2 photoadduct between the 2,3 double bond of khellin and the 5′, 6′ double bond of thymine. This behaviour is analogous to that of the furocoumarins and serves as a mechanism to describe the genotoxicity of the furochromones khellin and visnagin. These two compounds are phototoxic towards bacteria and fungi and inhibit mitosis and cause gross chromosomal changes in Chinese hamster ovary (CHO) cells in near UV light. For comparative purposes, 8‐methoxypsoralen was also tested and was found to be more active than visnagin which, in turn, was more active than

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb02677.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Photoproducts induced upon excitation of methotrexate by UV light have been separated by ion exchange chromatography. They include 2,4‐diamino‐6‐pteridinecarboxylic acid, 2,4‐diamino‐6‐pteridine‐carboxaldehyde and other unidentified pteridine derivatives. The same photoproducts can be also formed upon photodynamic reaction using hematoporphyrin as photosensitizer. In oxygen saturated aqueous solutions (pH∼7), methotrexate photoproducts sensitize the oxidation of histidine and tryptophan by UV light by a process involving singlet oxygen. In aqueous solutions containing albumin or in human serum, the same photoproducts are formed from free methotrexate but not from albumin‐bound methotrexate. In the latter case the results may suggest that methotrexate covalently binds to albumin upon excitation with UV light either in absence or in presence of oxygen. These results could explain the photosensitization accompanying cancer chemotherapy with high dose methotrexate and also the synergistic effects of PUVA + low dose methotrexate i

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb02678.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Upon irradiation with ultraviolet light the isoflavonoid phytoalexins phaseollin, 3,6a, 9‐trihydroxypterocarpan, glyceollin, tuberosin and pisatin, but not medicarpin, brought about inactivation ofglucose–6‐phosphate dehydrogenase in anin vitroassay system. Photoinactivation of the enzyme by photoactivated pisatin in air‐saturated solutions was hardly affected by singlet oxygen quenchers such as NaN3, bovine serum albumin, histidine or methionine. Neither addition of the hydroxyl radical scavengers mannitol, Na‐benzoate and ethanol nor the presence of catalase or supcroxide dismutase protected the enzyme against photoinactivation, suggesting that OH, H2O2and O2are not the reactive oxygen species involved. However, the free radical scavenger S‐(2‐amino‐ethyl)isothiouronium bromide hydrobromide (AET) protected the enzyme against inactivation by photoactivated pisatin. Direct evidence for the generation of free radicals was obtained by ESR measurements of solutions of phaseollin, pisatin and medicarpin in hexane irradiated with ultraviolet light in the presence or absence of O2. Phaseollin produced the most stable free radicals, whereas medicarpin hardly gave rise to free radical formation; pisatin took a somewhat intermediate position by producing a strong ESR signal which, however, decayed rather quickly. Photodegradation of all phytoalexins, except for medicarpin, was accompanied with loss of fungitoxicity, as shown in thin‐layer chromatographic bioassays, and formation of new products.These results indicate free radical formation as the causative process for photoinactivation of enzymes by photoactivated isofla

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb02679.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY