摘要:

Abstract—The rates of dye‐sensitized photooxidation of tyrosine and tyramine to brown products were compared in the presence and the absence of the anionic polysaccharide, alginate. The polyelectrolyte did not affect the reaction when it was sensitized by monochromatic light absorbed mainly by the monomeric form of the dye. In white light, the rate of oxidation sensitized by thionine or phenosafranine was increased in the presence of alginate for tyramine, but not for tyrosine. In the thionine sensitized reaction, the ratio of brown product formation to tyramine consumption increased with decreasing wavelength of monochromatic excitation. These and other phenomena are believed related to the formation of complexes between the dyes and some of the oxidation products, and to association between some of the oxidation products and alginate. A mechanism for oxidation of phenols is proposed, based on the addition of O2(1Δ9) across a double bondorthoto the phenolate oxygen. Dyes bind to alginate in monomeric and in aggregated forms; only the monomeric forms of thiazine dyes are photochemically active, but both the monomeric and the aggregated forms of crystal violet are ac

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06762.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—The thionine sensitized photooxidations of several tyrosine derivatives have been compared in a system in which the dye, bound to the anionic polysaccharide alginate, is separated by a dialysis membrane from a much larger external phase containing most of the substrate. Brown oxidation products appear both inside the bag and outside, but at considerably greater concentration inside. Oxidation products inside the bag retard the oxidation of the original substrate by competing with it for photooxidant. Substrates were divided into two groups, related to tyrosine and tyramine respectively, according to their rates of oxidation. The groups differ as to whether the prevailing phenolate form of the substrate is a zwitterion or an anion. In case of the latter, the Donnan equilibrium set up by the polyelectrolyte reduces its concentration in the polymer phase, and thereby the rate of oxidation. Titration and dialysis data support this interpretatio

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06763.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—The oxygen dependence of 365 nm inactivation of colony‐forming ability ofEscherichia colihas been investigated in two series of DNA repair‐deficient K12 mutants grown to mid‐exponential phase. All strains excepta uvr A recA double mutant are more sensitive to inactivation under O2and show a lower threshold dose. The inactivation of photoreactivating enzyme in a crude cell extract and DNA repair disruption are both reduced when irradiation is carried out under nitrogen. TherecA gene‐dependent synergism between 365 nm and ionising radiation is reversible if cells are incubated in full growth medium before ionising radiation treatment. In a wildtype strain, incubation for 2.5 h in full growth medium after 106J m‐2365 nm radiation changes a sensitised response to a protection from ionising radiation. Protection is not seen at 1.5 times 106J m‐2. A tentative model for near UV lethality in logarithmic phase cells is suggested which proposes two classes of lesions. One requires oxygen for it's induction, is rapidly fixed as a lethal event as a result of repair disruption, and is primarily responsible for cell death after aerobic 365 nm irradiation. The other lesion, possibly pyrimidine dimers, may lead to cell death under anaerob

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06764.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—Invivoparticipation of singlet excited oxygen (1O2,1Δ9) in the photodynamic inactivation and induction of genetic changes (gene conversion) in acridine orange‐sensitized yeast cells was investigated by using N3‐, an efficient1O2quencher, and D2O, a known agent for the enhancement of the lifetime of1O2. The addition of N3‐protected the cells from both photodynamic actions. From an analysis of the concentration‐dependent protection, about 80% of the induction of the genetic change is explainable on the basis of1O2mechanism. The quantitative estimation of the N3‐protection in the inactivation was not possible because of the sigmoidal nature of the inactivation curve. The replacement of H2O with D2O during illumination was effective in enhancing the photodynamic inactivation but almost completely ineffective for the gene conversion induction. The deuterium effect with the cell system was clearly not as large as would be expected fromin vitroexperiments. This, however, could be explained from the kinetic consideration that natural quenchers oflO2in the cell would mask the deuterium effect. By experiments with different cell stages it was demonstrated that these two modifying effects were dependent on the intracellular reaction environment. The conclusion is that1O2must be the major intermediate responsible for the photodynamic actions in acridine orangesensitized

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06765.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—The chemical modification of rabbit muscle aldolase by coupling with diazotizedp‐amino benzoate results in the preparation of a photosensitive enzyme. The photosensitivity is realized with the presence of arene diazothioether chromophores, due to the substitution on cysteine residues (eight groups per enzyme molecule). By absorption and emission spectroscopy it has been shown that at neutralpH visible light causes E→Z isomerization of the extrinsic chromophore. The reaction is thermally reversed with τ= 2.3 min at 24.3°C. Fading of the chromophore is observed after long irradiation time, especially in alkali solution; atpH 13 some of the diazo groups are exchanged with histidine residues to form azo derivatives of the imidazole anion. Optimum condition for photochromic behaviour of azoaldolase is irradiation with visible light centered at 450 nm, by using neutral solutions of the protein. Within the photochromic cycle slight differences have been observed in the gel electrophoretic behaviour of the azo

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06766.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—The use of competitive methods with rubrene as reference acceptor provides values of the rate constants kBQ= 2.3 times 109/ mol‐1s‐1and kvq= 3.3 times 109mol‐1s‐1for the physical quenching of O21δg, by bilirubin (in CCl4) and biliverdin (in CHCl3) respectively attributed to electron and energy transfer processes.The rate constant kBR= 1.7 times 108/ mol‐1s‐1for bilirubin reaction with O21δg is considerably greater than that kvR3 times 108mol‐s‐1for the reaction of biliverdin which has identical O21δa, acceptor sites, and is attributed to a primary Type I oxidation process followed by a slower Type II addition of O21δg to

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06767.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—Direct photooxidation of cyanine dyes was found to be markedly enhanced by formation of hypsochromically shifted (H) aggregates. Singlet oxygen was found to attack many cyanines possessing low oxidation potentials with rate constants in excess of 108t mol‐1s‐1. Singlet oxygen attack on 3,3′‐diethyl‐8,10‐dimethylthiacarbocyanine yields carbonyl products consistent with 1,2 addition to the 2,8 bond of the

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06768.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—Extremely high levels of paramagnetic manganese (Mn2+) which quench phosphorescent reactions have been found to inhibit the formation of thymine‐containing dimers inM. radiodurans. Lowering the concentration of Mn2+in the culture medium resulted in a lower intracellular concentration of Mn2+, an increase in the UV‐sensitivity of this bacterium, and a larger photochemical yield of thymine‐containing dimers. High levels of paramagnetic Mn2+were not found in other test organisms which are more sensitive to UV‐irradiation. One interpretation of our data is that inMicrococcus radioduransMn2+may bind to the chromosome and thereby reduce the photochemical yield of thymine‐contai

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06769.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—Phototaxis action spectra have been determined in three different types ofEuglena gracilis; green and dark‐bleached cells containing the stigma and streptomycin‐treated white mutant with an absorptionless stigma. In all three types of microorganisms the flavin containing paraflagellar body is present. The shape of the action spectrum is the same for the three types of cells and proportional to the absorption spectrum of flavoproteins. It has been shown that the structure of the action spectrum does not depend on the presence of screening organelles, on which, instead, depends the direction of the response to the light stimulus. It is concluded that the flavin chromophores present in the photoreceptor are the pigments responsible for phototaxis inEuglena gra

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06770.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—We present physiological evidence using the threshold control of lipoxygenase synthesis† by Pfrin the mustard seedling (LOG response) that there is no dark reversion of phytochromewhich would be relevant for this response. Such Ptr which can be detected with the lipoxygenase response disappears exclusively through degradation with a half‐life of 45 min at 25°C. De novo synthesis of P*rin the hypocotylar hook takes place at a constant rate (zero order rate constant) irrespective of the level of Pror P*tot, i.e. there is no detectable feedback control of Prsynthesis during the period of experimentation. The data of the present paper are consistent with a quantitative phytochrome model (Scheme 1) which has been advanced and treated quantitatively in the companion paper (Oelze‐Karow and Moh

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06771.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY