摘要:

AbstractPhase sensitive detection of fluorescence was used to directly record the initially excited and the solvent‐relaxed emission spectra of N‐acetyl‐L‐tryptophanamide in propylene glycol. Emission from the initially excited state was suppressed by adjusting the phase sensitive detector to be out of phase with the emission on the short wavelength side of the fluorescence spectrum. Then, the phase sensitive intensities revealed the emission spectrum of the solvent relaxed state. Similarly, the emission from the solvent relaxed state was suppressed by adjusting the detector to be out of phase with the emission on the long wavelength side of the spectrum, allowing the spectrum of the initially excited state to be directly recorded. Distinct emission spectra could be recorded when the solvent relaxation time was comparable to the fluorescence lifetime. At higher or lower temperatures, emission occurs predominantly from a single state, and suppression of the fluorescence signal at any arbitrary wavelength resulted in suppression of the entire emission. A simple theory is described which allows the spectral relaxation times to be estimated from the phase sensitive intensities. From this analysis we obtained an activation energy for spectral relaxation of 3 kcal/mol. This activation energy is smaller than that found for the temperature dependence of fluorescence depolarization, 7.8 kcal/mol. We attribute this difference to the smaller molecular motions required for spectral relaxation.The method of phase sensitive detection of fluorescence shows excellent resolving power and sensitivity, and this method should facilitate measurement of spectral relaxation around tryptophan residues in p

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04353.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThe fluorescence emission of iron‐free cytochromec(0Cytc) in a glassy matrix was investigated under conditions of very low temperature (4.2 K.) and narrow bandwidth laser excitation. Excitation into the vibronic band, Qx(1,0) resulted in highly resolved emission spectra of linewidth 10‐20 cm−1. Using the model of selective excitation developed by Abramel al.(1975) and McColganet al.(1978), the emission spectra of vibronic excitation afforded a method to investigate excited state vibrational structure. Furthermore, emission profiles have shown that in0Cytc, the site distribution (inhomogeneous broadening) has a width in the order of 20

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04354.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractLaser flash photolysis and pulse radiolysis have led to the characterisation of several shortlived intermediates formed after irradiation of retinoic acid and retinyl acetate in hexane or methanol.For retinoic acid, the triplet state, wavelength maximum 440 nm, extinction coefficient 7.3 × 104dm3mol−1cm−1, decay constant 6.2 × 105s−1, is formed with a quantum yield of 0.012 for 347 nm excitation. The radical cation, absorption maximum 590 nm, extinction coefficient ∼7 × 104dm3mol−1cm−1, is formed in a biphotonic process. The radical anion, absorption maximum 510nm in hexane, 480 nm in methanol where its extinction coefficient is 1.2 × 105dm3mol−1cm−1, appears to decay partially in methanol into another longer‐lived neutral radical, wavelength maximum 420 nm, by loss of OH−.For retinyl acetate, the triplet state, absorption maximum 395 nm, extinction coefficient 7.9 × 104dm3mol−1cm−1, decay constant 1.2 × 106s−1is formed with a quantum yield of 0.025 for 347 nm excitation. Monophotonic photoelimination of OCOCH3− in methanol produces the retinylic carbenium ion, wavelength maximum 590 nm, whose decay is enhanced by ammonia, k ∼ 2 × 106dm3mol−1s−1and retarded by water. The radical cation also has a wavelength maximum at 590 nm, its extinction coefficient being ∼ 1.0 × 105dm3mol1cm−1. The long‐lived transient absorption with maximum at 385 nm, extinction coefficient 1.0 × 105dm3mol−1cm−1, obtained from the reaction of the solvated electron with retinyl acetate in methanol may be due to either the radical anion itself or more likely the radical resulting from elimination of OCOCH3− from this anion.These results suggest that skin photosensitivity caused by retinyl a

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04355.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractCadmium(II), zinc(II), magnesium(II), and bis‐[thallium(I)] complexes ofmeso‐tetraphenyl‐porphyrin undergo unsensitized photooxygenation to yield a bilitriene derivative as the final product. The reaction has previously been shown to involve singlet oxygen (Matsuuraet al., 1980); on the basis of mass spectrometry of products from16O2and18O2experiments, and characterization of the initial photoproduct, the reaction is shown to proceed by a mechanism in which one oxygen molecule adds to the metalloporphyrin to give a metallobilitriene. In the subsequent work‐up, demetalation and addition of two hydrogen atoms gives the final

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04356.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThe photosynthetic electron transport inhibitor dibromothymoquinone was found to mediate the photoreduction of horse heart cytochrome c in aqueous solution. This process appears to involve the reduction of dibromothymoquinone to the corresponding hydroquinone followed by direct electron transfer to cytochromec.A subsequent‘autoxidation’of the reduced cytochrome c takes place which requires the presence of both oxygen and quinone. Irradiation of ethanolic stock solutions of dibromothymoquinone generates a hydroquinone species which is (1) capable of reducing cytochrome c directly in aqueous solution in the dark and (2) chemically distinct from the parent compound. This photore‐duced species is stabilized in ethanolic solution but undergoes autoxidation (t1/2= 24 s) when placed in an aqueous medium. Because dibromothymoquinone is used in photosynthetic studies, some care must be taken to avoid complications which might arise from the above reactions; suitable precautions are disc

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04357.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThe lysis of phosphatidylcholine (PC) liposomes was sensitized to visible light (>500nm) by hematoporphyrin (HP) incorporated in the liposomes (0.09‐1.5%, wt/wt) or in the external buffer (1‐15 μM). The lytic mechanism changed from the Type II pathway mediated by singlet oxygen (1O2) at low HP concentrations to the anoxic, Type I pathway at high HP concentrations. Spectral measurements of HP in aqueous and organic solvents indicate that the HP was not aggregated (monomers and/or dimers) for Type II sensitization and aggregated for Type I conditions. High concentrations of azide (>0.1M) or DABCO (>0.5M) were protective with high HP concentration under oxic and anoxic conditions, which cannot involve the scavenging of1O2. Feasible protective mechanisms are quenching of the HP triplet state by high azide and repair of the damaged membrane by DABCO via an electron transfer process. There was significant protection against lysis under Type I conditions by low concentrations of ferricyanide (>1 mM), indicative of an electron transfer mechanism. The incorporation of 22 mol % cholesterol in PC liposomes with 1% HP had no effect on the lytic efficiency for oxic and anoxic conditions. Dipalmitoylphosphatidylcholine liposomes incorporating 1% HP showed negligible photosensitized lysis at 50°C compared with PC liposomes with 1% HP at 25°C. The promotion of photosensitized lysis by hydrodynamic agitation observed in prior work with methylene blue (Grossweiner and Grossweiner, 1982) was significant with HP sensitization for both Type I and Type II conditions. Actinometry with PC liposomes incorporating 1% HP indicated that photosensitized lysis was very inefficient, requiring many absorbed quanta per lysed liposome. Preliminary experiments with crude hematoporphyrin derivative (Hpd) showed similar concentration effects on lytic efficiency, where PC liposomes incorporating 0.1% (wt/wt) Hpd were strongly sensitized by oxygen, whereas sensitization by oxygen was insignificant with 3.1% Hpd. The results with HP and crude Hpd indicate that lytic damage in a biomembrane does not necessarily require oxyge

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04358.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractA UV‐hypersensitive mutant of Chinese hamster ovary (CHO) cells, termed 43‐3B, has been used in a comparative study with the wild type CHO in order to determine the involvement of repair in several postirradiation phenomena. 43‐3B has the same growth rate and chromosome number as the wild type CHO‐9. It is hypersensitive to UV irradiation (D0of 0.3 J/m2as compared to 3.2 J/m2for the wild type). 43‐3B shows only about 17% of the UV‐stimulated unscheduled DNA repair synthesis of CHO‐9 as measured by autoradiography. When breaks in supercoiled chromatin are measured after UV by the nucleoid sedimentation method, the mutant appears to be capable of carrying out only limited incision. A much reduced ability to recover control rates of semiconservative DNA synthesis after UV irradiation was observed in the repair‐deficient 43‐3B cell line, suggesting that the removal of UV‐induced replication blocks by excision repair is the most important factor in allowing recovery of UV‐inhibited DNA synthesis. Recovery of colony‐forming ability between fractionated UV exposures was observed in the wild type CHO‐9, but little recovery was seen in 43‐3B. This indicates that excision repair capability can also be importan

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04359.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractIrradiation by UV‐A ofE. coliDNA polymerase I in the presence of 8‐methoxypsoralen (8‐MOP) leads to a similar inactivation of the 5′→ 3’polymerase and 3’→ 5’exonuclease activities of the enzyme. The kinetics of inactivation depend on the psoralen concentration and on the duration of irradiation. The 5′→3’exonuclease activity is first slightly stimulated at short irradiation time in the presence of 8‐MOP; further irradiation leads to inhibition of this activity. The mechanism of the reactions involves oxygen as shown by the absence of any effect of UV irradiation when oxygen is removed. The results obtained in D2O, in oxygen‐saturated buffer or in the presence of singlet oxygen (1O2) quenchers show that1O2is one of the reactive intermediate species. Irradiation of homopolymers primed with oligomers in the presence of 8‐MOP inhibits their template and initiating capacity in the same dose range as that required to inactivate DNA polymerase I. Mono‐adducts of 8‐MOP with nucleic acid bases can act as inhibitors o

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04360.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThe mechanism of action of the phototoxic polyacetylene phenylheptatriyne (PHT) against viruses was investigated. For this purpose the membrane containing mouse cytomegalovirus (MCMV) was treated with PHT in long wave UV light, and several functions of the virus were then examined. Following this treatment MCMV retained its structural integrity, as revealed by electron microscopy, resistance to exogenous deoxyribonuclease, and sedimentation‐velocity. The treated virus was also normal in its ability to penetrate into the nuclei of susceptible mouse cells. Replication of the virus was defective, however, in that infectious centers could not be established and no infectious progeny resulted. Two RNA‐containing viruses, Sindbis and infectious hematopoietic necrosis virus (IHNV, a fish virus), both of which contain membranes, were inactivated by PHT in long wave UV as efficiently as MCMV. In contrast, the fish virus IPNV (infectious pancreatic necrosis virus), which does not possess a membrane, was resistant to PHT. Thus, it appears that PHT, in the presence of long wave UV, exerts its action via the viral membrane and as a consequence the viral genome, DNA or RNA, is unable to replic

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04361.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThe action spectra for delayed erythema and melanogenesis in Caucasian human skin are determined for wavelengths between 250 and 435 nm. The untanned skin of very fair volunteers was observed after single exposures to a range of fluences of monochromatic radiation. At wavelengths longer than 300 nm the two action spectra are indistinguishable, and at wavelengths shorter than 300 nm, they are of similar shape despite a distinct separation. This suggests a common or similar chromophore for initiation of the vascular and pigmentary responses to UV. A broad minimum in the action spectra occurs near 280 nm, a maximum near 296 nm, and for wavelengths longer than 300 nm, increasingly larger fluences of radiation are required to induce delayed erythema and melanogenesis. Between 304 and 334 nm both action spectra exhibit a rapid decrease of almost three orders of magnitude. In contrast, between 334 and 405 nm the spectra decrease by only one order of magnitude, and there is a suggestion of a small maximum at or near 365 nm. Different chromophores, sites of damage, or response mechanisms may be responsible for induction of delayed erythema at these longer wavelengths. After spectral corrections for the optical effects of the stratum corneum, the shape and magnitude of the action spectra are grossly consistent with a mechanism in which DNA is the primary chromophore initiating the response pathways for wavelengths less than 313 nm. Whatever the actual basis for these action spectra may be, they are of practical significance in predicting skin response to sources of ultraviolet radiation.

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04362.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY