摘要:

AbstractThe photolysis of 5‐S‐cysteinyldopa, 2,5‐S,S‐dicysteinyldopa, 4‐hydroxybenzothiazole and cysteinyldopa melanins has been studied by ESR‐spin trapping methods using 5.5‐dimethyl‐1‐pyrroline‐1‐oxide and 2‐methyl‐2‐nitrosopropane as spin traps for hydrated electrons, hydrogen atoms, and carbon‐centered alanyl radicals. The photochemistry of these materials is shown to resemble dopa in that both photoionization and photohomolysis occur. However, unlike dopa, the cysteinyldopa also forms the carbon‐centered alanyl radicalsviaphotodecomposition of the cysteinyl group. Action spectra and quantum yields are reported. Mechanism(s) of

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05525.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe photochemistries of the melanin precursors dopa, 5‐S‐cysteinyldopa (5‐SCD) and 2.5‐S,S'‐dicysteinyldopa (2.5‐SCD) were investigated by 265‐nm laser flash photolysis. The quantum yield of hydrated electron following flash photolysis of dopa (9.1%) was half the yield of dopasemiquinone (19.6%), implying that dopasemiquinone is formedviatwo primary photochemical mechanisms: photionisation (giving e) or photohomolysis (giving H˙). Dopasemiquinone rapidly disproportionates to form dopaquinone and re‐form dopa. Dopaquinone in turn decaysviaa base‐catalysed unimolecular cyclisation eventually to form dopachrome. Assignment of the transient species was confirmed by previous pulse radiolysis studies of the one‐electron oxidation of dopa. In contrast, flash photolysis of the cysteinyldopas, 5‐SCD and 2,5‐SCD results in lower photoionisation quantum yields and the production of initial transient species whose absorption spectra were markedly different from their semiquinone absorption spectra previously determined pulse radiolytically. These observations indicate that the primary cysteinyldopa photochemical species is not such a semiquinone, but rather results from S‐CH2bond photohomolysis. Absorption spectra and rate constants for the formation and decay of various tran

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05526.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractCysteinyldopas, metabolic by‐products of activated melanocytes, are photochemically unstable in the presence of biologically relevant ultraviolet radiation (i.e. wavelengths>300 nm). Initial photochemical processes involve free radical production; continued photolysis yields polymeric photoproducts. Radicals produced during 5SCD photolysis were trapped by 5,5‐dimethyl‐l‐pyrrolidine‐l‐oxide (DMPO) and identified by their ESR spectra. Further characterization by use of nitroso spin trap (2‐methvl‐2‐nitrosopropane‐MNP) demonstrated that homolytic cleavage of the ‐S‐CH2bond of the 5SCD cysteinyl side chain is a significant photochemical pathway. The potential photobiological significance of these reactive intermediates was investigatedin vitrousing isolated nucleic acids. Radiolabeled 5‐[35S]‐cysteinyldopa was found to photobind to calf thymus DNA with 300 nm light activation. Under similar conditions, 5‐S‐cysteinyldopa also induced single strand breakage of3H‐radiolabeled superhelical, circular pBR322 plasmid DNA. The implications of the 5SCD photoinitiated DNA damage and the production of highly reactive free radicals in this process are discussed with respect to the etiology of various skin cancers

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05527.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractIn a reaction mixture containing hematoporphyrin derivative, deoxyribose, Fe3+‐EDTA and either methionine or tryptophan, hydroxyl radicals were formed during illumination with visible light. When either hematoporphyrin derivative, Fe3+‐EDTA or the amino acid was omitted from the reaction mixture, the generation of hydroxyl radicals ceased. These observations suggest an iron‐catalyzed Haber‐Weiss reaction, involving superoxide and hydrogen peroxide in the generation of hydroxyl radicals. It could be shown that with methionine H2O2was indeed an essential intermediate in the reaction sequence. With tryptophan, however, H2O2, was not generated. Apparently a photooxidation product of tryptophan could replace H2O2in the OH‐generating reaction with Fe2+‐EDTA. Although superoxide was generated in the reaction mixture, it was not an indispensable intermediate. Apparently a porphyrin radical, formedviaphotoexcitation of hematoporphyrin derivative, could replace superoxide in the Haber‐W

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05528.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractIn the presence of oxygen and visible light, various synthetic water‐soluble porphyrins cleave pBR 322 plasmid supercoiled DNA (form I) producing relaxed (form II) and linear (form III) DNA corresponding to single‐strand and double‐strand breaks respectively. Large variations are observed in the efficiency of the porphyrins containing a diamagnetic metal or no metal at all. Singlet oxygen (1O2) seems to be involved in the mechanism of cleavage consistent with the inhibitory effect of the azide anion, N–3. The higher efficiency of cationic porphyrins (as compared to anionic ones) is due to their greater affinity for DNA as shown by experiments carried out at either high ionic strength or in the presence of the surfactant, sodium dodecyl

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05529.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractPhotooxygenation reaction of an unsaturated fatty acid ester, methyl linoleate (methyl 9‐cis.12‐cis‐octadecadienoate, ML‐H), sensitized by porphyrins and several types of dyes has been studied in aqueous emulsion and acetonitrile solution under air at 40°C. The oxygen (O2) uptake proceeded slowly in the absence of sensitizers upon irradiation of an aqueous emulsion and an acetonitrile solution of ML‐H (20 mM) at ?ex>290 nm (11.4 and 6.1 μmol h‐1, respectively). The rate of O2uptake was enhanced by a catalytic amount (0.1 mM) of porphyrins and dyes; hematoporphyrin (HP), zinc tetrakis(N‐methyl‐4‐pyridiniumyi)porphyrin (ZnTMPyP), methylene blue (MB), rose bengal (RB), acridine orange (AO), and acriflavine (AF). In both systems, the sensitized photooxidation of ML‐H by O2proceeded equimolarly to produce isomeric mixture of C9 and C13 hydroperoxides having thetrans,cisandtrans,transconjugated diene configurations, independent of the types of the sensitizers used. The yield ratio oftrans,trans/ trans,cisproducts in the MB‐sensitized photooxygenation in acetonitrile and aqueous emulsion were almost equal (0.32 and 0.35. respectively). The sensitizing activity of the sensitizers, as measured by the quantum yield of O2uptake, increased in the order: MB (≃ 0)

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05530.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe room‐temperature optical properties of calf thymus DNA, with about 75% of its guanine residues methylated at position N‐7, are compared with those of 7‐methyl GMP which has the same fluorophore. The fluorescence spectrum of the methylated guanine residues depends strongly on the excitation wavelength, shifting to the blue as the wavelength increases. The fluorescence quantum yield, corrected for the contribution to absorption by the other virtually nonfluorescent residues, exhibits a pronounced drop at long excitation wavelengths relative to that for excitation at 265 nm. The degree of fluorescence polarization exhibits a weak dependence on the excitation and emission wavelengths. For 7‐methyl GMP, the fluorescence spectrum is very weakly dependent on the excitation wavelength and its fluorescence quantum yield shows a moderate increase at long wavelengths. The degree of fluorescence polarization increases with increasing excitation wavelength particularly when monitoring the emission in the short wavelength region of the fluorescence spectrum. A pronounced drop of unknown origin is observed when exciting at 265 nm, which is not observed for methylated DNA. The methylated DNA data are interpreted in terms of a combination of (i) a heterogeneous environment of the methylated guanine residues, which results from sequence‐dependent stacking interactions, and (ii) transfer of excitation energy from the other residues to the fluorescing methylated guanine residues. From the values of the quantum yields and those of the decay times, which we have recently reported (Georghiouet al., 1985), the following values are obtained for the radiative,kt, and the sum of the nonradiative, σk1, rate constants for deexcitation of the excited states of methylated DNA and its free fluorophore: 1.6 × 108s‐17 × 107s‐1and 5 × 1010s‐lvs6 × 109s‐1. Because of energy transfer from the other residues. thekfvalue for the methylated guanine residues is overestimated but their σk1, value is not affected significantly and is by about an order of magnitude larger than that for 7‐methyl GMP, apparently because

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05531.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractSpin label oximetry has been used to study the effects of photosensitizer hematoporphyrin on oxygen consumption in Chinese hamster ovary cells. These measurements demonstrate that, in the presence of the sensitizer, there occurs (i) an increase in total oxygen consumption during irradiation and (ii) a decrease in oxygen consumption following irradiation. These results are attributed to the effects of photosensitized oxygen consumption and decreased cellular respiration due to cell inactivation. Thus the inhibition of oxygen consumption after irradiation was shown to correlate with decreased cell survival measured in cell culture experiments. Possible mechanisms of inactivation and extensions of the oximetric approach are discussed.

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05532.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe photobinding of radiolabeled psoralen and 8‐methoxypsoralen (8‐MOP) to biological macromolecules under conditions that affect the lifetime of singlet oxygen (1O2) is reported. These conditions are: increase of1O2lifetime in D2O and1O2quenching with DABCO. The photobinding to calf thymus DNA was studiedin vitroand the covalent photobinding to DNA and other biological macromolecules (RNA, proteins) was also studied in intact bacteria. The results of the DNA photobinding experiments have been related to the induction of genetic damage in a bacterial test system. In addition, laser flash photolysis has been used to measure the effect of D2O and DABCO on the psoralen and 8‐MOP triplet lifetimes. In general D2O increases the triplet lifetimes and DABCO quenches the triplet states with the probable formation of radicals. The results suggest that the covalent photobinding of 8‐MOP to various biological macromoleculesin situis a basis for cell damage occurring at various cellular targets. Analysis of the results of the mutagenicity test suggests that in the presence of D2O the mechanism of induction of genetic lesions is not changed and therefore largely seems to be independent of singlet

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05533.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractFour Cockayne Syndrome (CS) lymphoblastoid lines were tested for the lethal effects of UV radiation (254 nm) with or without addition of exogenous β‐nicotinamide adenine dinucleotide (β‐NAD+) to their culture medium. Two of them exhibited a small but significantly increased resistance to UV radiation when β‐NAD+was added to the culture. However, their UV sensitivity after β‐NAD+addition was still much greater than that of normal control lines. Normal control lymphoblastoid lines and those from complementation group A and group C of xeroderma pigmentosum (XP) did not reveal any differences in post‐UV sensitivity after the addition of exogenous β‐NAD+. Thus the abnormal response to the lethal effects of UV radiation of CS lymphoblastoid lines could not be rectified by β‐NAD+addition. However, β‐NAD+does appear to play some partial role in reducing the high UV sensitivity of some C

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05534.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY