摘要:

AbstractOxidation of several lignin model compounds with alkylated paraphenolic groups by photosensitizing riboflavin (RF). rose bengal (RB) and methylene blue (MB) was examined. Photosensitizing RF cleaved l–(3‘‐4’‐diethoxyphenyl)‐1.3 dihydroxy‐2‐(4‐methoxyphenyl)propane (I). 4‐ethoxy‐3‐methoxyphenylglycerol‐(3‐guaiacyl ether (II) and l‐(4‘‐ethoxy‐3’‐methoxyphenyI)‐1,3 dihydroxypropane (IV) at their respective Cα‐Cβbonds. Riboflavin also oxidized 3.4‐diethoxy‐benzaldehyde (VI) to the corresponding acid, and hydroxylated the conjugated olefin l‐(4‘‐ethoxy‐3’‐methoxyphenyl)1.2 propene (III) to yield the initial product IV. In contrast, MB and RB hydroxylated III but had no effect on I, II, IV or VI under identical conditions. This suggested RF effected transformations via a hydrogen radical abstraction (Type I) rather than a1O2mediated reaction.To confirm this, the effects of deuterium oxide (D:0) and oxygen pressure on the photosensitizing dye reactions were examined. The effect of D20 on tryptophan (Trp) oxidation and hydroxylation of III by MB and RB was significant, indicating involvement of1O2. D2O had no significant effect on cleavage of the diarylpropane (I) and the olefin (III) by RF, indicating these reactions did not proceed by a Type II mechanism. While O2pressure effect on Trp oxidation by MB was insignificant, it had a large negative effect on cleavage of I by RF. These results, coupled with the relatively slow oxidation rate of Trp by RF. indicate that photosensitizing RF produces1O2inefficiently and is not effecting oxid

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb04426.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractThe photoexcited triplet states of the physically bound (intercalated) complexes of benzanthracene, pyrene, and free base porphin with DNA have been examined at 77 and 2 K. Measurements of triplet lifetimes, zero field splittings, and individual triplet sublevel intcrsystem crossing rates were obtained by optically detected zero field magnetic resonance (ODMR) for the benzan‐thracene‐DNA and free base porphin‐DNA complexes. The triplet lifetime was measured for the pyrene‐DNA complex. No ODMR was observable in the pyrene‐DNA system. Comparison of triplet state data with new and previous results for the benzo(a)pyrene‐DN A complex is discussed in an attempt to characterize the interactions experienced by polycyclic aromatic hydrocarbons and porphyrins within the DNA

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb04427.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractThe photodecomposition of sulfanilamide (4‐aminobenzenesulfonamide), sulfacetamide. sulfathiazole. sulfadiazine, carbutamide and tolbutamide has been studied using the spin traps 2‐methyl‐2‐nitrosopropanc and 5,5‐dimethyl‐l‐pyrroline‐l‐oxide. The following radicals were trapped during the photolysis of sulfanilamide in aqueous solution: H' and HNC6H4SO2NH, (α‐fission). SO2NH2and C6H4NH2(δ fission). H2NC6H4SO2and NH2(δ‐fission). Although the C.,H4SO2NH2and the SO; radicals were also detected these were not formed directly by homolytic bond fission. Homolytic bond fission was also observed during the irradiation of sulfacetamide (α.δ), sulfadiazine (α). carbutamide (α,δ) and tolbutamide (δ). All of the analogs, with the exception of tolbutamide, generated the SO; radical. Sulfacetamide, sulfadiazine and carbutamide generated the C6H4SO2;NHR radical by some process that did not involve homolytic bond fission. The free radicals generated by these agents may play an important role in their photot

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb04428.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract2‐Methylnaphthoquinone (MQ) has been excited in water with a 20 ns laser flash at 353 nm and the resultant transient species have been observed optically. Triplet‐state MQ (3MQ) decays on a sub‐microsecond time scale. It has been characterized in terms of its absorption spectrum and quantum yield. Rate constants have been measured for the decay of3MQ in infinitely dilute solution, for self‐quenching by ground‐state MQ, and for reactions of3MQ with oxygen, thymine, uracil, 6‐methyluracil, and orotic acid. The interaction of3MQ with pyrimidines involves charge transfer to give the pyrimidine cation radical and the MQ : anion radical. These reactions are discussed in relation to the mechanism of pyrimidine photooxidation sensi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb04429.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractUltraviolet radiation (δ>295 nm) induced covalent binding of anthracene to DNA which increased with time and was not affected by oxygen. Irradiation in the presence of anthracene induced nicking of Col E, circular DNA and decreased the thermal denaturation temperature of calf thymus DNA. These effects were oxygen dependent, and were decreased by GMP. Irradiation of anthracene and human serum albumin resulted in covalent binding of the hydrocarbon to the protein accompanied by crosslinking of the protein. Protein crosslinking decreased under anaerobic conditions. Irradiation of anthracene bound to liposomes induced lipid peroxidation which was not affected by superoxide dismutase or catalase

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb04430.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractThe wavelength dependence of inactivation and mutagenesis in the range between 254 and 313 nm was investigated in haploid cells of the yeastSaccharomyces cerevisiae.The action spectra for a wild type and an excision deficient mutant essentially corresponded to those for bacteria and mammalian cells. There were, however, minor differences. The ratio of mutagenic to lethal action decreased with increasing wavelength in the wild type, but remained constant in the excision deficient mutant. This is discussed in terms of error‐prone and erro‐free repair. For both inactivation and mutagensis, photorcactivability was lower with longer wavelengths in the wild type, but did not change in the excision deficient mutant. Implications for the role of pyrimidine dimers are conside

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb04431.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractBlue light induces the formation ofNeurospora crassaprotoperithecia.This photoinduction is completed in less than 24 h. Its threshold is about 4.2 J/m2. Red light is ineffective. The Bunsen‐Roscoe law is obeyed at the fluence of 12.6 J/m2for fluence rates from 5.25 × 102to 1.05 W/

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb04432.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract‐An animal experiment is presented which involved a total of 223 albino hairless mice (Skh hr 1). These mice, excluding 24 of them which served as controls, were divided over 6 groups, each of which received a different but constant daily dose of UV radiation from fluorescent sunlamps (Westinghouse FS40TL12). The range of daily doses encompassed a factor of 33. Data on the response of each group as a whole are presented. The group responses are measured in two ways: (1) the proportion of tumor bearing mice (prevalence), and (2) the average number of tumors per survivor (yield). The data provide information on the variation of the group response with time, daily dose and tumor size.The relationship between the daily dose and the duration of the treatment till 50% of the mice have tumors is given for several sizes of tumors. From these results, and from direct measurements of tumor growth, it appears that the growth of tumors is virtually dose‐independent and, in consequence, only the initiation of tumors is dose‐dependent. This implies that the theoretical model of UV‐tumorigenesis presented by Blum (1959). based on UV‐accelerated growth, is incorrect. It is pointed out that, in similarity to chemo‐ and radiotumorigenesis, the total dose delivered to a mouse for the induction of tumors has to be higher if a high daily dose is used than if a low daily dose is used. It seems as though an animal becomes more resistant to the UV‐stimuius as the rate at which the stimulus is presented is increased: an adapti

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb04433.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractClinical evidence indicates that people with light skin and red hair have a higher incidence of UV radiation‐induced diseases including cancer. It is not known whether this is because of the lower protection due to the smaller amounts of eumelanin present in the skin of these people or whether the presence of pheomelanin in their skin is responsible for the higher susceptibility to carcinogenesis. Irradiation of melanoproteins from red hair with UV‐visible light has been reported to produce superoxide. Comparative studies on the formation of superoxide during the irradiation of the melanins isolated from human black and red hair (BHM and RHM, respectively) are reported in this paper. These showed that no superoxide formation could be detected in the case of the BHM. whereas the formation of superoxide during the irradiation of RHM could be definitely demonstrated. Irradiation of the RHM with NADH resulted in the oxidation of more NADH than the irradiation of NADH with BHM. The observation that RHM is an active photosensitizer indicates that this property of pheomelanin present in light skin may at least partly be responsible for the harmful effect of radiation on people with light skin and/or red hair. Administration of hematoporphyrin followed by visible irradiation is a currently used mode of therapy for cancer. The present studies have shown that hematoporphyrin is bound to both BHM and RHM. The binding of hematoporphyrin to the melanins increased the formation of superoxide by RHM and the oxidation of NADH by both the melanins. The binding of porphyrins to melanins may have an influence upon the photosensitivity in diseases such as porphyrias and may also affect the therapeutic efficacy of hematoporphy

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb04434.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract‐Large phytochrome immobilized via anti‐phytochrome immunoglobulin bound to Sepharose beads was irradiated to saturation with unpolarized far‐red light. The apparent absorbance level was recorded in a dual wavelength spectrophotometer with both measuring beams set to either 660 or 730 nm and polarized perpendicular to each other. The sample was then irradiated with red polarized light. The apparent change in absorbance obtained after this irradiation indicated that purified phytochrome could show linear dichroism. From the absorbance values obtained it was computed that the direction of the long‐wavelength transition moment changes by either 32 or 148o, when phytochrome is transformed from Prto Pfr. Considering the model of Hahn and Song (1981) the latter value appears more likely. In light of these results, the conclusions drawn fromin vivoexperiments on action dichroism inDryopteris(Etzold, 1965),Adiantum(Kadotaet al.,1982) andMougeoutia(Haupt. 1970), which point to a 90orotation. should be recon

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb04435.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY