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Showing papers in "Photochemistry and Photobiology in 1983"


Journal ArticleDOI
TL;DR: In this article, the triplet oxygen quantum yield of 11 purified fluorescein derivatives was determined by reaction with singlet oxygen acceptors in aqueous and ethanolic solutions; in both solvents ϕ1o2 was enhanced with increasing halogenation.
Abstract: The singlet oxygen quantum yield (ϕ1o2) of 11 purified fluorescein derivatives was determined by reaction with singlet oxygen acceptors in aqueous and ethanolic solutions; in both solvents ϕ1o2 was enhanced with increasing halogenation. Tryptophan and 2,2,6,6-tetramethylpiperidone were found to be unadapted for the determination of ϕ1o2, in our systems; however, the use of 9.10-dipropionic anthracene acid andp-nitrosodimethylaniline in conjunction with imidazole derivatives was suitable for 1O2 detection in water. Both methods lead to results in excellent agreement. As in ethanol. ϕ1o2, was equal to the triplet state quantum yield (ϕT), the comparison between the two solvents showed that ϕT in water was greater than in ethanol. The comparison between our values obtained with polychromatic light with published data obtained with monochromatic light suggests that the triplet quantum yield of fluorescein derivatives is wavelength independent.

395 citations


Journal ArticleDOI
TL;DR: The superoxide dismutases found in plants resemble those encountered in other organisms as mentioned in this paper, where within chloroplasts one finds the CuZn enzyme, while mitochondria contain the Mn enzyme.
Abstract: In plants, as in other aerobic organisms, O2− is a commonly encountered intermediate of oxygen reduction and superoxide dismutases provide a defense against the potential cytotoxicity of this radical. The superoxide dismutases found in plants resemble those encountered in other organisms. Within chloroplasts one finds the CuZn enzyme, while mitochondria contain the Mn enzyme. Nymphaceae, ginkoaceae and cruciferae are unusual among plants, indeed among eukaryotes, in that they contain an iron superoxide dismutase. Bipyridylium herbicides, such as paraquat, exert their effect by diverting electron flow from photosystem I and thus increasing 02– production. Paraquat-resistant genotypes of horseweed, tobacco and rye grass were found to contain elevated superoxide dismutase. This enzyme also appears to provide a defense against sulfur dioxide, sunscald and photooxidative death. The evidence supporting these statements and possible explanations are discussed.

236 citations


Journal ArticleDOI
TL;DR: In this article, the optical properties of the human brain in the wave-length region from blue to near infrared are presented, and significant variations in the optical penetration depth from the neonatal and to the adult brain are shown.
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 larger.

224 citations


Journal ArticleDOI
TL;DR: The extinction coefficient of triplet benzophenone in benzene has been directly determined by absolute measurements of absorbed energy and triplet absorbance, deltaD/sup 0//sub T/, under demonstrably linear conditions where incident excitation energy, E/sub 0/, and ground state absorbance (A/Sub 0)/ are both extrapolated to zero as discussed by the authors.
Abstract: The extinction coefficient epsilon/sub T/, of triplet benzophenone in benzene has been directly determined by absolute measurements of absorbed energy and triplet absorbance, deltaD/sup 0//sub T/, under demonstrably linear conditions where incident excitation energy, E/sub 0/, and ground state absorbance, A/sub 0/, are both extrapolated to zero The result, 7220 +- 320 M/sup -1/ cm/sup -1/ at 530 nm, validates and corrects many measurements of triplet and radical extinctions and yields, using the energy-transfer method As E/sub 0/ and A/sub 0/ both decrease, deltaD/sup 0//sub T/ becomes proportional to their product In this situation, the ratio R = (1/A/sub 0/) (ddeltaD/sup 0//sub T//dE/sub 0/) = (epsilon/sub T/ /sup -/ epsilon/sub G/)phi/sub T/ Measurements of R, referred to benzophenone, give (epsilon/sub T/ - epsilon/sub G/)phi/sub T/ for any substance, without necessity for absolute energy calibration Both absolute and relative laser flash measurements on zinc tetraphenyl porphyrin (epsilon/sub T/ - epsilon/sub G/ at 470 nm = 73 x 10/sup 4/ M/sup -1/ cm/sup -1/) give phi/sub T/ = 083 +- 004 6 figures, 2 tables

159 citations


Journal ArticleDOI
TL;DR: In this paper, a study was designed to separate the immediate effects of visible radiation on UV-B photosynthetic inhibition from the indirect influence of visible irradiation on morphological and physiological properties of leaves during leaf development.
Abstract: — Visible radiation can substantially influence the degree to which plant photosynthesis is inhibited by UV-B radiation. This study was designed to separate the immediate effects of visible radiation on UV-B photosynthetic inhibition from the indirect influence of visible irradiation on morphological and physiological properties of leaves during leaf development. Soybean plants were pretreated in growth chambers with either high or low visible irradiance (750 and 70 μmol m-2s-1 quantum flux in the 400–700 nm waveband, respectively) during the development of leaves used subsequently for UV irradiation. Test leaves still attached to the plant were exposed to 5 h of polychromatic UV-B irradiation and the photosynthetic capacity (net CO2 exchange) was determined before and after the UV irradiation. During the UV irradiation, plants from both pretreatment groups received either high or low visible flux. Development of leaves in the high visible flux pretreatment conditions resulted in thicker leaves, higher chlorophyll a/b ratios, more UV-absorbing pigments, and reduced sensitivity to the UV-B irradiation. However, higher visible flux during the UV-B irradiation resulted in greater depression of photosynthesis by the UV-B irradiation. The relative magnitude of photosynthetic depression under these treatment combinations was the same when photosynthesis was measured under either light-limited or light-saturated conditions.

138 citations


Journal ArticleDOI
TL;DR: A control system is described which allows lamp emittance to be modulated over a large dynamic range (50:1), permits stable lamp operation and starting at low temperatures, and provides a sensitive feedback loop to compensate for both atmospheric conditions, such as cloud cover, as well as changes in radiant emittance from the lamps resulting from factors such as temperature and lamp age.
Abstract: Precise control and modulation of fluorescent sunlamps are necessary for ecologically valid simulation of solar UV-B (280-320 nm) radiation enhancement which would correspond to ozone reduction. A control system is described which allows lamp emittance to be modulated over a large dynamic range (50:1), permits stable lamp operation and starting at low temperatures, and provides a sensitive feedback loop to compensate for both atmospheric conditions, such as cloud cover, as well as changes in radiant emittance from the lamps resulting from factors such as temperature and lamp age.

135 citations


Journal ArticleDOI
TL;DR: The action spectrum for DNA strand breakage was found to exhibit one peak at 265 nm, consistent with DNA absorption, and a second peak at 450 nm, similar to the normalized absorption spectrum for riboflavin, a known photosensitizing agent, implicating this molecule as the absorbing chromophore.
Abstract: — The induction of DNA single-strand breaks in normal human fibroblasts exposed to monochromatic wavelengths from 240–546 nm was measured by the alkaline elution assay. The cells were irradiated at 1°C to prevent both repair of induced breaks and formation of enzymatically induced breaks through excision repair. The cultures were also washed with and irradiated while suspended in phosphate buffered saline to prevent the formation of DNA damaging photoproducts from medium components. The action spectrum for DNA strand breakage was found to exhibit one peak at 265 nm, consistent with DNA absorption, and a second peak at 450 nm. The normalized action spectrum in the visible is similar to the normalized absorption spectrum for riboflavin, a known photosensitizing agent, implicating this molecule as the absorbing chromophore.

118 citations


Journal ArticleDOI
TL;DR: 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 adaptive phenomenon.
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 adaptive phenomenon.

117 citations


Journal ArticleDOI
A. Kawski1
TL;DR: In this paper, it was shown that the rate of radiationless excitation energy transfer in isotropic media is related to the probability of the emission and absorption transitions in the interacting molecules.
Abstract: The problem of radiationless electronic excitation energy transfer in isotropic media has lost none of its interest although it has been under investigation for more than 50 years. On the grounds of classical physics, Perrin (1925) had already predicted that the electromagnetic field of an excited oscillator would induce forced oscillations of an unexcited oscillator at the same frequencies, considering the interacting molecules as linear oscillators, thus resulting in energy transfer from an excited to an unexcited molecule. Such a process of energy transfer occurs when the separation between the interacting oscillators is not large (up to about 10 nm), when their oscillations are approximately equivalent. The theory of Perrin (1925). as well as its quantummechanical modification (Perrin, 1932), did not yield results consistent with experimental data. The quantum-mechanical theory of very weak interactions in isotropic media was later developed by Forster (1946, 1948a), Galanin (1955) and Dexter (1953), who demonstrated that the rate of energy transfer could be related to the probability of the emission and absorption transitions in the interacting molecules. According to Forster (1948a), the rate of radiationless excitation energy transfer, pDA, is given by

110 citations


Journal ArticleDOI
TL;DR: Those preparations of Hp which contain, as an impurity, a porphyrin similar to that found to be responsible for the tumor photosensitizing ability of Hpd, may be effective photosensitizers of tumors but are generally of low efficacy.
Abstract: — The ability of hematoporphyrin (Hp) to act as a photosensitizer of cells in vitro or in vivo is a matter of dispute, while hematoporphyrin derivative (Hpd), a mixture of porphyrins including hematoporphyrin, has been consistently found to be an effective photosensitizer both in vitro and in vivo. Until recently the actual component of the Hpd mixture responsible for these effects had not been identified. We have found that those preparations of Hp which contain, as an impurity, a porphyrin similar to that found to be responsible for the tumor photosensitizing ability of Hpd, may be effective photosensitizers of tumors but are generally of low efficacy. This material accounts for the entire photosensitizing activity of both Hp and Hpd in the SMT-F mammary carcinoma in DBA/2 HeHa mice.

110 citations


Journal ArticleDOI
TL;DR: This review discusses important developments in the area of photosensitization from approximately June, 1982, through June, 1983, including studies with animal and human cells in culture.
Abstract: This review discusses important developments in the area of photosensitization from approximately June, 1982, through June, 1983. For the most part the articles cited will represent in vitro work, including studies with animal and human cells in culture. The review is divided into three sections dealing with the following classes of photosensitizing dyes and pigments: (1) porphyrins; (2) furocoumarins; (3) miscellaneous (including, e.g. flavins, xanthenes, and thiazines).

Journal ArticleDOI
TL;DR: In this paper, the photo properties of the triplet (T) states of hematoporphyrin (HP) and coproporphrin (CP), particularly in relation to their medium dependence and reactivity towards oxygen, were investigated.
Abstract: — This paper describes an experimental study of the photo properties of the triplet (T,) states of hematoporphyrin (HP) and coproporphyrin (CP), particularly in relation to their medium dependence and reactivity towards oxygen. Triplet-triplet absorption spectra of HP and CP have been determined in aqueous buffer at pH = 7.4 and in water-methanol and water-formamide mixtures. The spectra corrected for ground state contributions show major absorption peaks near 400 nm and lesser peaks near 500 nm. Extinction coefficient measurements have been made and their dependences on solvent composition investigated. Natural lifetimes of the T1 states of HP and CP and the bimolecular quenching constants with oxygen have been determined. The quantum yields of T1 formation are ca. 0.6 in buffer rising to 0.8 and higher in predominantly organic media. Incorporation of the porphyrins into micellar phases similarly causes φT, to increase. Quantum efficiencies of O−2 and O2(lΔg) formation have been determined for HP in buffer, some binary mixtures and micellar dispersions. Superoxide yields are low and may result from photo-ionization processes. O2(lΔg) yields are large but appear to have an unexpected dependence on the medium.

Journal ArticleDOI
TL;DR: Light regulation attained by state transitions is produced by the state II–I transition induced by system I light, and the dark state was identified to be state II.
Abstract: Time courses of state I-state II transitions were measured in the thermophilic blue-green alga (Cyanobacterium), Synechococcus lividus, that was grown at 55°C. The rate of the state I–II transition using light II illumination was the same as that in the dark, and the dark state was identified to be state II. Therefore, light regulation attained by state transitions is produced by the state II–I transition induced by system I light. The redox level of plastoquinone did not affect this dark state II. Arrhenius plots of the state transitions showed a break point around 43°C that corresponded to the phase transition temperature of this alga. Since both the state I–II and II–I transitions were very much temperature-independent, we could keep the alga in either state for a long time at a “low” temperature such as room temperature. Activities of both photosystems I and II in states I and II were also measured. After a state II–I transition, the system II activity increased about 16% and at the same time, svstem I activity decreased about 30%.

Journal ArticleDOI
TL;DR: A commonality in the UVR chromophores of mice and men as they relate to the acute responses described, and a direct additivity of effectiveness from the U VR components in a polychromatic beam, at least over the portion of the Uvr spectrum tested (λ > 295 nm).
Abstract: The hairless mouse has been used as an experimental model for photocarcinogenesis for about 20 years. Although the carcinogenesis action spectra for mice and man are not known, acute responses to ultraviolet radiation (UVR) in the biologically active UVB and UVC region (wavelengths below 320 nm) can be compared. Vascular response (predominantly edema) action spectra for monochromatic radiation in the Skh:HR-l (albino hairless) male mouse were determined. These action spectra were found to be very similar to the human erythema action spectrum that had been developed using the same monochromator. The accuracy of this experimentally derived action spectrum was tested with a series of polychromatic source spectra. The mice were exposed to radiation from a long arc Xe lamp filtered by varying thicknesses of Schott WG320 filters, which yielded a wide range of biologically effective spectra. Spectral irradiance measurements, when weighted with the mouse edema and human erythema action spectra and multiplied by the irradiation time required to elicit a threshold response (edema), yielded a constant weighted dose regardless of irradiation spectral quality. The integrated effective dose was approximately 200 J/m2 of 297 nm equivalent energy, agreeing with requirements for the monochromatic 297 nm dose in the mice as well as for minimal human erythema. These data suggest a commonality in the UVR chromophores of mice and men as they relate to the acute responses described, and a direct additivity of effectiveness from the UVR components in a polychromatic beam, at least over the portion of the UVR spectrum tested (λ > 295 nm).

Journal ArticleDOI
TL;DR: This Yearly Review covers the literature published about five different photopigments in halobacteria during 1982 and until about June 1983 and might be of general interest for those working in this research field.
Abstract: Halobacteria became interesting again after the role of bacteriorhodopsin (BR) in light-energy convers ion h a d b e e n d i s c o v e r e d ( B l a u r o c k a n d Stoeckenius, 1971; Oesterhelt and Stoeckenius, 1971). It turned out that they are suitable objects for studying various aspects of photoenergy transformation, photosensory transduction, and other problems in membrane biology. Halobacterium halobium and other extremely halophilic bacteria form distinct patches in the surface membrane when grown under semiaerobic conditions and illumination. These so-called purple membranes contain, besides the lipids (which make up about 25% of the total mass), only one type of protein: bacteriorhodopsin. Bacteriorhodopsin exhibits some similarities to the visual pigment rhodopsin. It contains the chromophore all-trans or 1 3 4 s retinal, which is covalently linked to a lysine residue of the protein moiety (molecular weight 26800) by a Schiff base and is responsible for the characteristic purple colour. During extensive investigation of the light-driven electrogenic proton pump bacteriorhodopsin, four additional retinal protein pigments have been discovered in halobacteria: the light-driven electrogenic chloride pump halorhodopsin (HR) (Matsuno-Yagi and Mukohata, 1977; Schobert and Lanyi, 1982), the photosensoric pigments P 565 and P 370 (Hildebrand and Dencher. 1975; Dencher, 1978; Sperling and Schimz, 1980) and the “slow-cycling rhodopsin” or “slow rhodopsin-like pigment” (SR) (Bogomolni and Spudich. 1982; Tsuda et a/. , 1982). This Yearly Review covers the literature published about these five different photopigments during 1982 and until about June 1983. Before then, the subject has been comprehensively surveyed by Stoeckenius and Bogomolni (1982). In addition more specialized reviews dealing with the primary events in the photochemistry of bacteriorhodopsin (Callender, 1982; Ebrey, 1982; Honig, 1982a,b) and with the various lightdependent active transport processes in halobacteria (Knaff and Davidson, 1982) have appeared. Fur thermore , in Volume 88 of Methods in Enzymology (1982), 137 authors describe in 91 articles the application of numerous biological, chemical and physical methods and strategies to the retinal-pigments in halobacteria and artificial systems. Most articles include a summary of the results obtained and therefore this book might be of general interest for those working in this research field, especially since some results are not yet published elsewhere. The molecular biological and biochemical aspects of archaebacteria to which the genus Halobacterium belongs have been previously summarized (Archaebacteria, 1982).

Journal ArticleDOI
TL;DR: The high sensitivity of the fluorescence detection makes it possible to use 4‐methylumbelliferyl substrates for the enzymes contained in a single cell, leading to enzyme release accompanying strong morphological changes.
Abstract: — The photodynamically-induced liberation of lysosomal enzymes using s-galactosidase as marker for the lysosomal enzymes has been studied by microspectrofluorometry on mouse L cells. Similar studies have been carried out using N-acetyl-s-D-glucosaminidase as marker for the lysosomal enzymes of human fibroblasts. The high sensitivity of the fluorescence detection makes it possible to use 4-methylumbelliferyl substrates for the enzymes contained in a single cell. Methylene blue and hematoporphyrin readily incorporate into both cells and upon excitation, sensitize lysosomal membrane damages, leading to enzyme release accompanying strong morphological changes.

Journal ArticleDOI
TL;DR: Blue light induces the formation of Neurospora crassa protoperithecia and the Bunsen‐Roscoe law is obeyed at the fluence of 12.6 J/m2.
Abstract: Blue light induces the formation of Neurospora crassa protoperithecia.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/m2 for fluence rates from 5.25 × 10 2 to 1.05 W/m2.

Journal ArticleDOI
TL;DR: Results are consistent with pyrimidine dimers induced in DNA being the major lethal lesion in both cell strains over the wavelength range 254‐313 nm, however, it is indicated that different mechanisms of inactivation operate at wavelengths longer than 313 nm.
Abstract: —Action spectra for UV-induced lethality as measured by colony forming ability were determined both for a normal human skin fibroblast strain (lBR) and for an excision deficient xeroderma pigmentosum strain (XP4LO) assigned to complementation group A using 7 monochromatic wavelengths in the range 254-365 nm. The relative sensitivity of the XP strain compared to the normal skin fibroblasts shows a marked decrease at wavelengths longer than 313 nm. changing from a ratio of about 20 at the shorter wavelengths to just greater than 1.0 at the longer wavelengths. The action spectra thus indicate that the influence on cell inactivation of the DNA repair defect associated with XP cells is decreased and almost reaches zero at longer UV wavelengths. This would occur, for example, if the importance of pyrimidine dimers as the lethal lesion decreased with increasing wavelength. In common with other studies both in bacterial and mammalian cells, our results are consistent with pyrimidine dimers induced in DNA being the major lethal lesion in both cell strains over the wavelength range 254-313 nm. However, it is indicated that different mechanisms of inactivation operate at wavelengths longer than 313 nm.

Journal ArticleDOI
TL;DR: In this article, the apical region of vertically position protonemata with small beams (0.2 mm) of red light induced a growth response towards the irradiated side (positive phototropism).
Abstract: — Protonemata of the moss Ceratodon purpureus cultured in white light were transferred to darkness for 3 days and then used for phototropic experiments. Irradiation of the apical region of vertically position protonemata with small beams (0.2 mm) of red light induced a growth response towards the irradiated side (positive phototropism). The phototropic response showed irradiance dependence. The effect of red light was completely reversed by far-red light following red light irradiations, demonstrating that phytochrome was the photoreceptor pigment. Far-red light or UV-blue light had no influence on either bulging or phototropism. Experiments with linearly polarized red or far-red light showed a different dichroic distribution of phytochrome in its different forms, the red-absorbing form, Pr and the far-red-absorbing form, Pfr. Red light with a vibration plane parallel to the long axis of the filaments was most effective. The effectiveness of far-red light was expressed best when its vibration plane was 90° to the electrical vector of the inductive red light.

Journal ArticleDOI
TL;DR: In this article, single-photon timing measurements on flowing samples of Chlorella vulgaris and Chlamydomonas reinhardtii at low excitation intensities at room temperature indicate two main kinetic components of the fluorescence at open reaction centers (F0) of photosystem II with lifetimes of approx. 130 and 500 ps and relative yields of about 30 and 70%.
Abstract: Single-photon timing measurements on flowing samples of Chlorella vulgaris and Chlamydomonas reinhardtii at low excitation intensities at room temperature indicate two main kinetic components of the fluorescence at open reaction centers (F0) of photosystem II with lifetimes of approx. 130 and 500 ps and relative yields of about 30 and 70%. Closing the reaction centers progressively by preincubation of the algae with increasing concentrations of 3-(3′,4′-dichlorophenyl)-l,l-dimethylurea (DCMU) and hydroxylamine gave rise to a slow component with a lifetime increasing from 1.4 to 2.2 ns (Fmax) The yield of the slow component increased to 65-68% of the total fluorescence yield in parallel to a decrease in the yield of the fast component to a value close to zero at the fmax-level. The 130 ps lifetime of the fast component remained unchanged. The middle component showed an increase of its lifetime from 500 to 1100 ps and of its yield by a factor of 1.5. Spacing of the ps laser pulses by 12 μs allowed us to resolve a new long-lived fluorescence component of very small amplitude which is ascribed to a small amount of chlorophyll not connected to functional antennae. The opposite dependence of the yield of the fast and the slow component on the state of the reaction centers at almost constant lifetimes is consistent with a mechanism of energy conversion in largely separately functioning photosystem II units. Yields and lifetimes of these two components are in agreement with the high quantum yield of photosynthesis. The lower lifetime limit of 1.4 ns of the slow component is assigned to the average transfer time of an excited state from a closed to a neighboring open reaction center and the increase in the lifetime to 2.2 ns is evidence for a limited energy transfer between photosystems II. Relative effects of changing the excitation wavelength from 630 to 652 nm on the relative fluorescence yields of the kinetic components were studied at the fluorescence wavelengths 682, 703 and 730 nm. Our data indicate that (i) the middle component has its fluorescence maximum at shorter wavelength than the fast component and (ii) that the antennae chlorophylls giving rise to the middle component are preferentially excited by 652 nm light. It is concluded that the middle component originates from the light-harvesting chlorophyll alb protein complexes and the major portion of the fast component from the chlorophyll a antennae of open photosystem II reaction centers.

Journal ArticleDOI
TL;DR: In this article, the 4-bromo-l-naphthoyl group was shown to be able to display its phosphorescence even under 1 atm of oxygen.
Abstract: The phosphorescence of the 4-bromo-l-naphthoyl group is readily quenched by molecular oxygen in homogeneous solvents. However, when this lumophore is complexed with γ-cyclodextrin in aqueous solution at room temperature, its phosphorescence is observed even under 1 atm of oxygen! Phosphorescence decay data indicated that two types of probe/cyclodcxtrin complexes are formed with lifetimes of 600 u,s and 3.5 ms. Oxygen completely quenches the fast decay, but only partially quenches the slow decay.

Journal ArticleDOI
Paul Galland1
TL;DR: A model of the sensory transduction chain is presented, which incorporates the fluence‐response curves of the bending angle and the aiming error angle indicate more than one receptor pigment for phototropism.
Abstract: Photogeotropic equilibrium action spectra in the range from 301 to 740 nm were made for Phycomyces wild type and the three behavioral mutants C47 (madA35), C109 (madBlOl) and LI (madCIIQ), all of which have a raised phototropic threshold. In addition to two broad peaks at 365 and 455 nm, typical for flavins, the wild type action spectrum shows three novel peaks, which have not been observed previously. These peaks are located at 414, 491 and 650 nm. The 650 nm peak has a relative quantum efficiency of 3 × 10−8 compared to the peak at 414 nm. The wavelength dependent shapes of the fluence-response curves of the bending angle and the aiming error angle indicate more than one receptor pigment for phototropism. The shape of the action spectrum of C47 is basically unaltered in comparison to wild type. C109 and LI show substantial differences from the wild type. In the near UV two small peaks at 334 and 365 nm appear; the 414 and 491 nm peaks present in wild type and C47 are missing and two new peaks at 529 nm (not well resolved in C109) and 567 nm are found. None of the three mad mutations affects the 650 nm peak. A model of the sensory transduction chain is presented, which incorporates these and other known features.

Journal ArticleDOI
TL;DR: Nanosecond laser flash photolysis and pulse radiolysis have been used to generate and characterise the triplet state, and semioxidised and semireduced radicals of haematoporphyrin and three 0‐acyl compounds derived from it.
Abstract: — Nanosecond laser flash photolysis and pulse radiolysis have been used to generate and characterise the triplet state, and semioxidised and semireduced radicals of haematoporphyrin, and three 0-acyl compounds derived from it (the monoacetate, the diacetate and the disuccinate). After 347 nm irradiation in water containing 2% Triton X-100, haematoporphyrin forms the triplet state (φT= 0.92) and photoionises monophotonically (φI= 0.03). For the O-acyl derivatives, φT approaches unity and photoionisation is reduced. In acetone the triplet yield of all four compounds are close to unity. The difference and corrected spectra for the triplet species are presented and decay rates (k1˜104s-1) and oxygen quenching constants (kQ˜1.5times109M-1s-1) for the triplet state have been measured. The difference and corrected spectra for the semi-reduced species in methanol and semi-oxidised species in aqueous Triton X-100 are presented. The photophysical characteristics in fluid solution of haematoporphyrin and its 0-acyl derivatives are rather similar to those previously recorded for other photosensitising porphyrins.

Journal ArticleDOI
TL;DR: The technique was shown to be useful in measuring Tδ values in several microheterogeneous systems such as surfactant micelles, vesicles and human serum albumin and the singlet oxygen lifetimes determined directly agreed well with published values.
Abstract: -The luminescence at 1.27 μm from the 31δg transition of the oxygen molecule has been detected from a variety of liquid systems. A Q-switched laser delivering pulses of 532 nm light was the excitation source, a germanium photodiode was the detector and substituted porphyrins were used as photosensitizers. Protio- and deutero- forms of several solvents were studied and the singlet oxygen lifetimes determined directly agreed well with published values. Tδ in D2O was found to be 55 μs and, by extrapolation from a series of H2O - D2O mixtures, a value of 3.3 μs was obtained for Tδ in H2O. The technique was shown to be useful in measuring Tδ values in several microheterogeneous systems such as surfactant micelles, vesicles and human serum albumin.

Journal ArticleDOI
TL;DR: Comparative studies on the formation of superoxide during the irradiation of the melanins isolated from human black and red hair (BHM and RHM, respectively) showed that no superoxide formation could be detected in the case of the BHM, whereas the formationOf superoxide During the irradiated of RHM could be definitely demonstrated.
Abstract: Clinical 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 hematoporphyrin.

Journal ArticleDOI
TL;DR: Findings suggest that both oxygen‐dependent and oxygen‐independent processes may be important in the phototoxic reactions of benoxaprofen.
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 reactions of benoxaprofen.

Journal ArticleDOI
TL;DR: In this article, the photosensitizing activities of hematoporphyrin, Cu-hematoporphrin, protoporphynin, Zn-protoporphin, deuteroporphrin and uroporphrin are studied.
Abstract: The photosensitizing activities of hematoporphyrin, Cu-hematoporphyrin, protoporphyrin. Zn-protoporphyrin, deuteroporphyrin and uroporphyrin are studied. The relative yields of 1O2 are measured in buffer (pH 8.0) and compared to the yields of Type II photodamages induced on cholesterol embedded in egg lecithin liposomes. Results show that the solubilization of the sensitizer in the lipid bilayer is a prerequisite for its photosensitizing activity at the membrane level. In this context, the partition coefficient represents an important parameter.

Journal ArticleDOI
TL;DR: 2‐Methylnaphthoquinone has been excited in water with a 20 ns laser flash at 353 nm and the resultant transient species have been observed optically and the interaction of 3MQ with pyrimidines involves charge transfer to give the pyrimidine cation radical and the MQ : anion radical.
Abstract: 2-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 of 3MQ in infinitely dilute solution, for self-quenching by ground-state MQ, and for reactions of 3MQ with oxygen, thymine, uracil, 6-methyluracil, and orotic acid. The interaction of 3MQ 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 sensitized by MQ.

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TL;DR: Five psoralens, at concentrations up to 500 times greater than those required to inactivate conventional viruses, did not influence scrapie agent titers in partially purified preparations from murine spleen and hamster brain.
Abstract: –In searching for a nucleic acid within the scrapie agent, we employed psoralens which penetrate the coats of most conventional viruses, form photoadducts with their genomes, and block replication of the viruses. Five psoralens, at concentrations up to 500 times greater than those required to inactivate conventional viruses, did not influence scrapie agent titers in partially purified preparations from murine spleen and hamster brain. 3H-psoralens were used to monitor the formation of photoadducts within nucleic acid standards added to preparations of the scrapie agent. Since no inhibition of psoralen photoadduct formation was observed in these preparations, one of three possibilities seems likely: the scrapie agent is devoid of nucleic acid, the psoralens failed to penetrate the protein coat of the agent, or its nucleic acid is unreactive with psoralens.

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TL;DR: Light‐induced movement responses of the heterotrichous ciliate Blepharisma japonicum were studied by physiological experiments and it was shown that only the anterior part of the ciliate is able to perceive the light stimulus that mediates the phobic reaction.
Abstract: Light-induced movement responses of the heterotrichous ciliate Blepharisma japonicum were studied by physiological experiments. Two photosensory responses could be identified. A step-up photophobic response is observed as a very rapid backward movement. Microbeam irradiations of individual cells showed that only the anterior part of the ciliate is able to perceive the light stimulus that mediates the phobic reaction. The action spectrum peaks at approximately 400 nm, which indicates that a blue light receptor is involved. Positive photokinesis of Blepharisma could be shown as a forward movement that is accelerated by increasing the applied photon fluence rate. The steady state level of the velocity depends highly on wavelength and photon fluence rate of the actinic light. After specific inhibition of the phobic reaction bv 1 m/W NH4+, photokinesis can be induced by microbeam irradiation at any part of the cell. We isolated two main pigments by thin layer chromatography and characterized them as hypericin-like compounds: a red pigment that is obviously responsible for the red color of the ciliates (= blepharismin). and a yellow one with maximal absorption near 420 nm. The possible photoreceptor functions of these pigments are discussed. We could not find in Blepharisma a distinct phototactic behavior which is so typical for the related ciliate Stentor.