Showing papers in "Photochemistry and Photobiology in 1976"
TL;DR: Evidence is developing for interesting interand intra-phyletic similarities, especially in the structure of luciferins and the chemiluminescent reaction mechanisms.
Abstract: In the past there has been emphasis on the view that bioluminescent systems exhibit considerable diversity, both biologically and chemically [55]. While this certainly remains so, evidence is developing for interesting interand intra-phyletic similarities, especially in the structure of luciferins and the chemiluminescent reaction mechanisms. Bacteria. Although the reaction mechanism in bacteria is distinctly different from other well characterized systems, cross phyletic relationships between bacteria and other forms do occur. Luminous bacteria 'inhabit' other phyla; they are known to occur as symbionts in fish and other higher organisms [55), and thereby provide the host organism with a light source which may be used for one or more specific functions. The flashlight fish (Photohlepharon palpebratus), which possesses a pair of light organs situated just beneath the eyes, is a recently studied example [93]. (These fish are now on exhibit a t the Steinhart Aquarium in San Francisco.) Leiognathid fish, with internal luminous organs, have also been investigated [15,57, 581. The ability to luminesce occurs in several groups of marine bacteria, whose systematic relationships to each other and to nonluminous marine bacteria were described in detail by Reichelt and Baumann [ 105,1061. Luminous bacteria which are symbiotic fall within the genus Photobacteriurn; bacteria in the Beneckea genus have not been found in a symbiotic relationship and are generally isolated from seawater (K. Nealson and J. W. Hastings, unpublished). A more specific habitat for and function of the luminescence in the Beneckea species have not yet been uncovered. Insight concerning the function of the light emission is emerging from studies of the control of the synthesis of the luminescent system. In both Photobacterium and Beneckea species, luciferase is not synthesized constitutively [58, 951. A substance (termed autoinducer) synthesized by the cells themselves accumulates in the medium and results in the induction of luciferase synthesis [41]. By radioactive labeling, 5 peptides have been isolated which are specifically synthesized during the induction period [%I. From studies of mutants which require exogenous aldehyde for luminescence (see below), it was concluded that at least two genes are specifically involved in the in t.im biosynthesis of aldehyde factor for luminescence and that both genes are coordinately controlled with that for luciferase [29]. Luciferase synthesis is also subject to repression by glucose, reversible by cyclic
528 citations
TL;DR: The kinetic properties of the area growth after firing a single saturating flash proved to be incompatible with the predictions of the “sequential double reduction” model, and results obtained were corroborated by results obtained from a kinetic analysis from the area restoration process in the dark, and an analysis of the partially restored areas.
Abstract: — In 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) poisoned chloroplasts of algae and‘ higher plants the area over the fluorescence induction curve increases with biphasic first order kinetics (Melis and Homann, 1975). Two possibilities are considered to explain the biphasic nature of the area growth. The first is a sequential double reduction of the primary electron acceptor in system II while the second envisages a heterogeneity of its photochemical centers. The kinetic properties of the area growth after firing a single saturating flash proved to be incompatible with the predictions of the “sequential double reduction” model. This conclusion was corroborated by results obtained from a kinetic analysis of the area restoration process in the dark, and an analysis of the partially restored areas.
Assuming an existence of a heterogeneous pool of photochemical centers, the growth of the area over the fluorescence curve could be further analyzed to yield two components, a fast a-component, and a relatively slow β-component. The kinetic characteristics of these components, and the effect of a short saturating flash on their respective size, led to the conclusion that one type of photochemical center had a faster recombination rate of the photochemically separated charges and was less efficient in trapping excitation energy.
270 citations
TL;DR: A meter for measuring the skin sunburn effectiveness of a light source is being used in an extensive network to provide solar data for correlation to skin cancer incidence so that the output correlates with ozone thickness.
Abstract: — A meter for measuring the skin sunburn effectiveness of a light source is being used in an extensive network to provide solar data for correlation to skin cancer incidence. The solar radiation measured also affects a wide variety of organisms. The intensity of this band of radiation is also strongly affected by ozone concentration so that the output correlates with ozone thickness.
The meter spectral response is essentially the excitation spectrum of magnesium tungstate phosphor which is similar to the erythema action spectrum (EAS). In addition to the waterproofed, dose reading embodiment, a cheaper, easily transportable, batteryless, intensity reading meter with the same spectral response has been developed.
The deviation of any sunburn meter from the ideal erythema action spectrum can be calculated by convolution of a series of solar spectra against each of the two response spectra. Plotting the change in output against the change in input results in straight lines. Either log-log coordinates are required, or, as is done here, decibels can be used on linear coordinates. The angle between the straight lines is taken as the error. An error angle of 6.5° is calculated for the present meter.
238 citations
TL;DR: It is concluded that the flavin chromophores present in the photoreceptor are the pigments responsible for phototaxis in Euglena gracilis.
Abstract: —Phototaxis action spectra have been determined in three different types of Euglena 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 in Euglena gracilis.
175 citations
TL;DR: In this review, the variety of extraretinally‐mediated responses has been described, and the physiological properties and anatomical location ofExtraretinal photoreceptors have been briefly discussed, to deepen the understanding of its place in the sensory armamentarium.
Abstract: It is clearly established that in birds, as in the other lower vertebrates, brain photoreception is a critically important perceptual mode. In this review, the variety of extraretinally-mediated responses has been described, and the physiological properties and anatomical location of extraretinal photoreceptors have been briefly discussed. In order to deepen our understanding of its place in the sensory armamentarium, several unresolved problems have been pointed out.
146 citations
TL;DR: It is suggested that the sensitisation to X‐rays seen in the HeLa cells after 365 nm treatment is not the result of lesions induced in DNA by the near‐UV radiation, but may reflect the disruption of DNA‐repair systems.
Abstract: — The colony-forming ability of Chinese hamster cells (V-79) and HeLa cells has been measured after near-ultraviolet (UV) irradiation, predominantly at 365 nm. To avoid the production of toxic photoproducts, cells were irradiated in an inorganic buffer rather than in tissue culture medium. Under these circumstances near-UV lethality was strongly oxygen-dependent. Both cell lines were approximately 104 times more sensitive to 254 nm irradiation than to 365 nm radiation when irradiated aerobically. Pretreatment with 6 times 105 Jm-2 365 nm radiation sensitised the HeLa, but not the V-79 cell line to subsequent X-irradiation. Pretreatment of cells with 17 Jm-2 254 nm radiation, a dose calculated to produce twenty times more pyrimidine dimers than the 365 nm dose, produced only slight sensitisa-tion to X-rays. It is suggested that the sensitisation to X-rays seen in the HeLa cells after 365 nm treatment is not the result of lesions induced in DNA by the near-UV radiation, but may reflect the disruption of DNA-repair systems.
121 citations
TL;DR: The natural photosynthetic quantum-capturing mechanism of some plants may provide a design for a synthetic system that will serve as a renewable resource for material and fuel as discussed by the authors, which is called WDM.
Abstract: The natural photosynthetic quantum-capturing mechanism of some plants may provide a design for a synthetic system that will serve as a renewable resource for material and fuel. (WDM)
113 citations
TL;DR: Evidence supports the interpretation that lesions induced in DNA by 365 nm and 460 nm radiations play the major role in the inactivation of E. coli by these wavelengths.
Abstract: — In stationary phase, strains of Escherichia coli deficient in excision (B/r Her) or recombination repair (K.12 AB2463) were more sensitive than a repair proficient strain (B/r) to monochromatic near-ultraviolet (365 nm) and visible (460 nm) radiations. The relative increase in sensitivity of mutants deficient in excision or recombination repair, in comparision to the wildtype, was less at 365 nm than at 254 nm. However, a strain deficient in both excision and recombination repair (K12 AB2480) showed a large, almost equal, increase in sensitivity over mutants deficient in either excision or recombination repair at 365 nm and 254 nm. All strains tested were highly resistant to 650 nm radiation. Action spectra for lethality of strains B/r and B/r Her in stationary phase reveal small peaks or shoulders in the 330–340, 400–410 and 490–510 nm wavelength ranges. The presence of 5μg/ml acriflavine (an inhibitor of repair) in the plating medium greatly increased the sensitivity of strain B/r to radiation at 254, 365 and 460 nm, while strains E. coli B/r Her and K12 AB2463 were sensitized by small amounts. At each of the wavelengths tested, acriflavine in the plating medium had at most a small effect on E. coli K.12 AB2480. Acriflavine failed to sensitize any strain tested at 650 nm. Evidence supports the interpretation that lesions induced in DNA by 365 nm and 460 nm radiations play the major role in the inactivation of E. coli by these wavelengths. Single-strand breaks (or alkali-labile bonds), but not pyrimidine dimers are candidates for the lethal DNA lesions in uvrA and repair proficient strains. At high fluences lethality may be enhanced by damage to the excision and recombination repair systems.
106 citations
TL;DR: In this paper, the spin selectivity of the reverse electron transfer process within the intermediate charge transfer complexes is discussed in terms of the spin-selectivity of Bph* and BphT in the presence of 8 M methyl iodide and 40 mMp-benzoquinone.
Abstract: — Nanosecond and picosecond. kinetic techniques have been used to study electron transfer from the first excited singlet state (Bph*) and the first excited triplet state (BphT) of bacteriopheophytin to p-benzoquinone. Quenching of the first excited singlet state by 40 mMp-benzoquinone results in a decrease in the lifetime of Bph* but does not lead directly to the formation of the π-cation radical (Bph†). In the presence of 8 M methyl iodide and 40 mMp-benzoquinone together, the singlet lifetime is reduced further; however, the quantum yield of BphT is enhanced due to the increased rate of intersystem crossing between Bph* and BphT. Electron transfer from BphT to p-benzoquinone leads to the formation and detection of Bph†. The results are discussed in terms of the spin-selectivity of the reverse electron transfer process within the intermediate charge transfer complexes.
92 citations
TL;DR: Comparison of the carotenoid triplet energy levels with that of O2('Δg) suggests that spirilloxanthin, spheroidene and possibly alsoζ‐carotene, would be expected to protect against photodynamic action caused by O2 ('Γg), but not cis or trans phytoene.
Abstract: — Absorptions of the triplet excited states of five carotenoids (15,15'-ds phytoene, all-trans phytoene, C-carotene, spheroidene and spirilloxanthin), extracted from the photosynthetic bacteria Rhodopseudomonas spheroides and Rhodospirillum rubrum, have been detected in solution using pulse radiolysis and laser flash photolysis. Triplet lifetimes, extinction coefficients, lowest energy levels and quantum efficiencies of formation have been determined. Comparison of the carotenoid triplet energy levels with that of O2('Δg) suggests that spirilloxanthin, spheroidene and possibly alsoζ-carotene, would be expected to protect against photodynamic action caused by O2 ('Δg), but not cis or trans phytoene. The S→T intersystem crossing efficiences of all five polyenes were found to be low, being a few per cent or less. In their protective role these triplet states can only therefore be effectively reached via energy transfer from another triplet, except in the case of O2 ('Δg). The low crossover efficiencies also mean that light absorbed by such carotenoids in their possible role as accessory pigments would not be wasted in crossing over to the triplet state.
91 citations
TL;DR: Ciliary reversal appears to be produced whenever the photic receptor potential crosses the threshold for elicitation of the regenerative response in the blue‐green ciliate.
Abstract: — The blue-green ciliate. Stentor coeruleus, is found predominantly in shady places. This concentration occurs because stentor responds when swimming from a shaded area to a lighted area by reversing the direction of its ciliary beat and reorienting its swimming direction until it once again is in the shaded area. A graded receptor potential is recorded from microelectrodes in vacuoles of stentor when the animal is photically stimulated. For all but very weak stimuli this receptor potential is sufficient to elicit a regenerative transmembrane response of variable amplitude in a swimming animal. Suprathreshold electrical stimuli also elicit this regenerative response. In turn the regenerative response is coupled to ciliary reversal. Thus ciliary reversal appears to be produced whenever the photic receptor potential crosses the threshold for elicitation of the regenerative response.
Using the threshold for production of ciliary reversal as a criterion response, an action spectrum was obtained. This action spectrum correlates well with the absorption spectrum of the major pigment of S. coeruleus, stentorin. Stentor bleached of pigment also have an elevated threshold for ciliary reversal. Thus stentorin seems to be the photosensitive pigment in stentor responsible for its photophobic behavior.
TL;DR: A new route suitable for preparing psoralen and many of its derivatives has been described by Queval and Bisagni and a semi-synthetic route to Psoralen, starting from marmesin, by Loutfy and Abu-ShadyC381 is described.
Abstract: A few studies have been devoted to the synthesis of new psoralen derivatives. A new route suitable for preparing psoralen and many of its derivatives has been described by Queval and Bisagni[56] and a semi-synthetic route to psoralen, starting from marmesin, by Loutfy and Abu-ShadyC381. Many new synthetic derivatives of psoralen have been prepared by Loutfy et al. [373 for testing their photosensitizing activity on skin and further investigating the relationship between chemical structure and photobiological activity. Some other tricyclic compounds (i.e. pyranocoumarins such as xanthyletin and dimethylallylxanthyletin) having structure analogous to furocoumarins, have been studied as to their possible photosensitizing activity and the ability to photoreact with DNA. These compounds appear to photosensitize biological substrates and able to form -both monoadducts and cross-linkings in double stranded DNA [22].
TL;DR: In this article, the reduction of the triplet state of methylene blue by both alkyl- and aryl-amines was studied, and it was concluded that reaction of amines with amines leads to the formation of a partial charge-transfer intermediate which may undergo complete electron transfer to yield radicals, or undergo spin inversion and return to the ground state.
Abstract: — Flash photolysis was used to study the reduction of the triplet state of methylene blue by both alkyl- and aryl-amines. The extent of the formation of the semireduced form of the dye yielded rate constants of interaction between the triplet state and the amine (k5). A correlation between log k5 and ionization potentials for alkylamines (slope = -1.75 eV-1) was interpreted as evidence for the formation of a partial charge-transfer intermediate. The rate constants (k5) calculated for aryl-amines approached the rate of diffusion in many cases. A Hammett plot for a series of N, N-dimethyl-anilines yielded a moderately large p value (– 3.28) consistent with the formation of a charge-transfer intermediate. It was concluded that reaction of amines with triplet methylene blue leads to the formation of a partial charge-transfer intermediate which may undergo complete electron transfer to yield radicals, or undergo spin inversion and return to the ground state.
TL;DR: Direct photooxidation of cyanine dyes was found to be markedly enhanced by formation of hypsochromically shifted (H) aggregates bysinglet oxygen attack on 3,3′‐diethyl‐8,10‐dimethylthiacarbocyanine yields carbonyl products consistent with 1,2 addition to the 2,8 bond of the methine chain.
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 108 t mol-1 s-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 methine chain.
TL;DR: Amphibians possess extraocular photoreceptors (EOPs) which exclusively or together with the lateral eyes perceive light for various physiological and behavioral activities and Photopigments have been identified for some of these responses.
Abstract: Amphibians possess extraocular photoreceptors (EOPs) which exclusively or together with the lateral eyes perceive light for various physiological and behavioral activities. Several kinds of EOPs are discussed but emphasis is given to the pineal complex: the dermal frontal organ (or stirnorgan) found only in frogs and toads among amphibians and the intracranial pineal body (or epiphysis cerebri) found in all Amphibia. Both structures are derived as dorsal evaginations of the diencephalon and have a retina-like fine structure. Both are sensitive to visible and UV light but not to IR, mechanical or chemical stimuli. The frontal organ gives chromatic and achromatic responses but in most species only achromatic ones are recorded from the pineal. Photopigments have been identified for some of these responses.
Pineal EOPs are involved in several activities: (i) neurosecretory activity by the subcommissural organ in the brain; (ii) body-lightening reaction in larval amphibians, involving the light-inhibited release by the pineal of a hormone, presumably melatonin, which contracts melanophores in the skin; (iii) cuing of circadian locomotor rhythms, including phase shifts and synchronization with environmental light cycles; (iv) perception of celestial cues for use in time-compensated compass orientation; and (v) possibly perception of linearly-polarized light.
Non-pineal EOPs have been implicated in (i) tail-darkening reaction of frog larvae where light has a direct effect on melanophores; and (ii) in phototaxis where unknown EOPs in various parts of the body and tail mediate withdrawal from light. Evidence for use of pineal and non-pineal EOPs and location of specific receptors is reviewed drawn from biochemical, ultrastructural, neurophysiological and behavioral studies. The possible use of EOPs for other biological functions and their possible adaptive value are briefly discussed.
TL;DR: Action spectra confirm the role of flavin in the photoreduction of cytochrome c and the photostimulation of oxygen uptake as a possible model system for similar photoreactions which have been observed in vivo.
Abstract: — The photoreduction of cytochrome c and the photostimulation of oxygen uptake were studied in solutions of flavin and cytochrome as a possible model system for similar photoreactions which have been observed in vivo. Light causes the photoreduction of the flavin. Under aerobic conditions the photoreduced flavin reacts with oxygen to form the superoxide anion which in turn can reduce cytochrome c. Dismutation of the superoxide anions forms hydrogen peroxide which mediates the dark oxidation of the photoreduced cytochrome. Superoxide formation and dismutation also account for the light-induced oxygen uptake. Action spectra confirm the role of flavin in the photoreduction of cytochrome c and the photostimulation of oxygen uptake. Under anaerobic conditions the photoreduced flavin reduces cytochrome c directly. In the presence of an electron donor only catalytic amounts of flavin are required. In the absence of an added electron donor flavin itself can act as the electron donor if substrate amounts are present. Azide inhibits all of these flavin-mediated photoresponses. Azide also inhibits the photoreduction of cytochrome b which occurs in the mycelium of Newospora.
TL;DR: In this article, the integrated dosages, based on the erythemal sensitivity curve and on the Robertson-Berger sunburn meter sensitivity curve, have also been calculated, and these are found to vary with latitude and season in very nearly the same way as 307 and 314 nm radiation, respectively.
Abstract: Tabulated values are presented for ultraviolet radiation at the earth's surface as a function of wavelength, latitude, and season, for clear sky and seasonally and latitudinally averaged ozone amounts. These tabulations can be combined with any biological sensitivity function in order to obtain the seasonal and latitudinal variation of the corresponding effective doses. The integrated dosages, based on the erythemal sensitivity curve and on the Robertson-Berger sunburn-meter sensitivity curve, have also been calculated, and these are found to vary with latitude and season in very nearly the same way as 307 and 314 nm radiation, respectively.
TL;DR: It is reported that both tryptophan photoproducts and H2O2 sensitize phage DNA to near‐UV radiation resulting in enhanced killing as well as enhanced DNA breakages and it is concluded that the in situ production of H 2O2 via tryPTophan photolysis may be an important biological event.
Abstract: — Near-UV irradiation of l-tryptophan yields a large number of photoproducts. When this mixture is added to recombinationless (rec) mutants of bacteria, the cells are killed. The most toxic component of tryptophan photoproducts has been identified as hydrogen peroxide (H2O2). We now report that both tryptophan photoproducts and H2O2 sensitize phage DNA to near-UV radiation resulting in enhanced killing as well as enhanced DNA breakages. We conclude that the in situ production of H2O2 via tryptophan photolysis may be an important biological event.
TL;DR: Daily exposure to photoreactivating radiation (> 315nm) following UV‐B insult mitigated the potentially lethal damage to the tadpole population.
Abstract: — Effects of increased intensity of UV-B radiation (290–315nm) on the systemic development and viability of boreal toad tadpoles were studied. When compared with animals exposed to UV-B deficient radiation of similar irradiance, tadpoles exposed to UV-B enhanced radiation displayed (1) abnormal development of the presumptive cornea, (2) areas of hyperplasia in the integument, (3) an anomalous, concave curvature of the spine, and (4) increased mortality. Daily exposure to photoreactivating radiation (> 315nm) following UV-B insult mitigated the potentially lethal damage to the tadpole population.
TL;DR: The concentration of Escherichia coli in the input and output of a tertiary wastewater system (4 lagoons) has been monitored over an 11 month period and it is possible to compare the ‘die off’ expected from solar UV exposure to the actual 'die off' observed for different batches of water.
Abstract: — The concentration of Escherichia coli in the input and output of a tertiary wastewater system (4 lagoons) has been monitored over an 11 month period. The integrated flux of biologically active solar ultraviolet (UV) radiation was measured during this period. By also determining (1) the effective temperature in the system, (2) the growth rate of E. coli at the effective temperature, (3) the penetration of the solar UV into the lagoons, (4) the dose-response relation for killing of E. coli by UV and (5) the retention time of water in the system, it is possible to compare the ‘die off’ expected from solar UV exposure to the actual ‘die off’ observed for different batches of water.
The observed killing of E. coli was quite close to the values calculated, considering the numerous factors involved. Solar UV light would thus seem to be a very important factor in the natural purification of water. Because each successful species must possess characteristics (physiological or behavioral) which provide adequate resistance to solar UV, the ecological role of solar UV radiation has not been widely appreciated.
TL;DR: In this article, the effects of pH, temperature and solvent deuteration on the fluorescence spectra and quantum yields of 7-azaindole and other model compounds in ethanol and in water are reported.
Abstract: — The fluorescence spectrum of 7-azaindole in alcohol is composed of two fluorescence bands. Effects of pH, temperature and solvent deuteration on the fluorescence spectra and quantum yields of 7-azaindole and other model compounds in ethanol and in water are reported. The long wavelength band arises from a tautomeric species formed in an adiabatic photoreaction involving double proton transfer between one molecule of 7-azaindole and one molecule of alcohol.
The fluorescence spectrum of 7-azaindole in water is composed of only one band, but the emission is weak and shows a large solvent isotope effect. The possibility of a double proton transfer reaction between 7-azaindole and water is discussed.
TL;DR: In this paper, the results are consistent with a mechanism in which singlet oxygen is produced by energy transfer from methylene blue triplet in the aqueous phase, and then diffuses to and penetrates the interior of the micelles where it reacts with the furan.
Abstract: — Oxygenated aqueous solutions of methylene blue containing dispersions of sodium dodecyl sulphate micelles with solubilised diphenyl isobenzofuran were irradiated with red light and the rate of loss of furan was followed over several min. The results are consistent with a mechanism in which singlet oxygen is produced by energy transfer from methylene blue triplet in the aqueous phase, and then diffuses to and penetrates the interior of the micelles where it reacts with the furan. The competition between this process and the natural decay of the excited oxygen has been examined and a β-value of 9.7 times 10-5M determined which is comparable to that for the same reaction in homogeneous solvents. A model of the system is proposed and its kinetic features discussed.
TL;DR: Extraretinal photoreceptors are widespread among insects and function in the photoperiodic control of development and in the entrainment of circadian rhythms, and in all studies to date they appear to be associated with the cerebral lobe region of the brain.
Abstract: — Extraretinal photoreceptors are widespread among insects and function in the photoperiodic control of development and in the entrainment of circadian rhythms. The effects of light on the daily and seasonal regulation of brain neuroendocrine activity are mediated solely through extraretinal photoreceptors. In primitive insects, the eyes participate in the entrainment of nonendocrine circadian rhythms such as the locomotor rhythm. In more advanced forms, however, extraretinal pathways appear to be the only pathway for the entrainment of all rhythms thus far examined. But even in this latter case, the eyes sometimes effect a masking of the expression of the overt rhythm. An exact localization of the extraretinal receptors has not been accomplished, but in all studies to date they appear to be associated with the cerebral lobe region of the brain. Action spectra for photoperiodic responses have been determined for a number of insects. In general the responses are maximally sensitive in the blue with a marked decline in the red although exceptions do exist. Complete action spectra for circadian responses have been determined only for two insects. In both cases a plateau of sensitivity extends through the blue with a steep drop at longer wavelengths. From the action spectra data, the extraretinal receptors appear to have a threshold sensitivity less than 3 times 10-2 J/m2. The pigment nature of the receptor is unknown although it appears not to be a carotenoid derivative.
TL;DR: From curves measured for the delay phase shift of pupae emergence of Drosophila pseudoobscura, an action spectrum was determined; it suggests a flavin to be the photoreceptor pigment.
Abstract: — Dose-response curves were measured for the delay phase shift of pupae emergence of Drosophila pseudoobscura. From these curves an action spectrum was determined for this process; it suggests a flavin to be the photoreceptor pigment.
TL;DR: It is concluded that the degree of hydration rather than the conformational state is the critical factor in determining which of the photoproducts will form in native DNA.
Abstract: — In an ethanolic solution native T7 DNA can undergo conformational transitions from the B conformation (0% ethanol) to the C-like (60% w/w ethanol) and the A (80% w/w ethanol) conformations. We have investigated the formation of three classes of thymine-derived photoproducts in T7 DNA irradiated (280 nm) in the B, C-like, and A conformations, which were monitored by circular dichroism measurements. We find that the predominant class of thymine-derived photoproducts in any conformational state is cyclobutyl dipyrimidines. While the ‘spore product,’ 5-thyminyl-5,6-dihydrothymine, which belongs to another class of photoproductsf does form in native DNA in the A conformation, its yield in denatured DNA at 80% ethanol is the same as that in native DNA. The yield of pyrimidine adduct, a third photoproduct class, is a maximum at 50–60% ethanol. This effect of ethanol is probably not due to the ethanol-induced C-like conformation, however, since pyrimidine adduct formation is not enhanced when T7 DNA is irradiated in the C conformation in 6 M CsCl or in intact phage. We conclude from these and other data in the literature that the degree of hydration rather than the conformational state is the critical factor in determining which of the photoproducts will form in native DNA.
TL;DR: The technique of forming bilayer lipid membranes (BLM) has made it possible to study photoreactions of pigments in an environment that is much closer to those in photosynthetic and visual membranes, and photoelectric effects due to coupled interfacial charge transfer reactions are illustrated.
Abstract: — The technique of forming bilayer lipid membranes (BLM) has made it possible to study photoreactions of pigments in an environment that is much closer to those in photosynthetic and visual membranes. A pigmented BLM system with Mg2+-porphyrins as membrane-bound pigments and with ferricyanide and ferrocyanide as the aqueous electron acceptor and donor, respectively, was used to illustrate the photoelectric effects due to coupled interfacial charge transfer reactions.
The steady-state continuous photoresponse was studied by means of the voltage clamp method and a null current method. The independence of the pigment conductance channel and the ionic conductance channel was demonstrated. A tunable voltage clamp method was used to study the transient pulsed photoresponses. Such a measurement permits us to characterize the photosystem in terms of an equivalent circuit model which contains a novel chemical capacitance. Molecular interpretation of this equivalent circuit model was given.
A microscopic model based on the Gouy–Chapman theory and chemical kinetics calculation leads to an equivalent circuit which is also equivalent to the previous one. Generalization of this microscopic model further leads to a physical mechanism of the generation of the early receptor potential (ERP) in visual membranes. Relevance of pigmented BLM research to photosynthesis and other disciplines was also discussed.
TL;DR: In this paper, the quantum efficiency of bacteriochlorophyll photo-oxidation in reaction centers from Rhodopseudomonas sphaeroides is independent of temperature, within experimental accuracy of ± 15%, from 300 K to 5 K.
Abstract: Abstract— The quantum efficiency of bacteriochlorophyll photo‐oxidation in reaction centers from Rhodopseudomonas sphaeroides is independent of temperature, within experimental accuracy of ± 15%, from 300 K to 5 K. Absorption spectra at low temperature show maxima at 532 and 544 nm corresponding to the two molecules of bacteriopheophytin in the reaction center. Comparison with the spectrum of the transient light‐induced state PF indicates that of these two molecules, only the one absorbing at 544 nm participates in forming PF.
TL;DR: There was an inverse correlation between culture age and population doubling level and photosensitivity, but this effect could not be related to capacity for DNA synthesis and cell division.
Abstract: — The damaging effects of near ultraviolet and visible light on WI-38 human diploid lung fibroblasts were investigated. WI-38 cells in culture were killed by light doses ranging from 2 to 10 × 103 W/m2 h. There was an inverse correlation between culture age, i.e. population doubling level and photosensitivity. However, this effect could not be related to capacity for DNA synthesis and cell division.
Flavins were clearly implicated as endogenous photosensitizers, and antioxidants such as d, l-α-tocopherol (vitamin E), BHT and ascorbic acid were found to afford the cells protection from light damage. Furthermore, products of lipid peroxidation could be detected in cell homogenates irradiated in the presence of ribofiavin.
TL;DR: The sea slug, Aplysia, is a useful model system for research on the neurophysiology of circadian integration and there is no evidence yet for hormonal coupling between photoreceptors and oscillators or between oscillators and rhythmic outputs.
Abstract: The sea slug, Aplysia, is a useful model system for research on the neurophysiology of circadian integration. The animal contains several circadian oscillators and several photoreceptors. Each eye contains a circadian oscillator as well as photoreceptors. The ocular oscillators can be entrained by extraocular photoreceptors as well as their own ocular photoreceptors. The abdominal ganglion probably contains another oscillator but it has been much more difficult to manipulate in the laboratory than have the oscillators in the eyes. There is also a circadian rhythm in overt behavioral activity. This rhythm is controlled in part by extraocular oscillators and extraocular photoreceptors and in part by the eyes. In exerting their influence on the behavioral rhythm, the eyes appear to act in the capacity of oscillators and not merely as photoreceptors. Although neurons in the retina have neurosecretory morphology, the entire influence of the eyes on the behavioral rhythm appears to be mediated by nerve signals which travel in the optic nerve. As yet there is no evidence to suggest that any two oscillators in Aplysia are internally coupled. There is also no evidence yet for hormonal coupling between photoreceptors and oscillators or between oscillators and rhythmic outputs.
TL;DR: The spectral distributions of two previously reported weak luminescences from liquid cultures of the yeast Saccharomyces cerevisiae have been determined and the UV components are compared with Gurwitsch's mitogenetic radiation.
Abstract: — The spectral distributions of two previously reported weak luminescences from liquid cultures of the yeast Saccharomyces cerevisiae have been determined. During the logarithmic phase of growth, emission was observed as a broad UV band between 200 and 425 nm, and as a visible region band between 525 and 700 nm. During the stationary phase, there were two narrow bands centred at 250 and 650 nm, and a broad band extending from 325 to 525 nm. The UV components are compared with Gurwitsch's mitogenetic radiation, and possible chemical and radiolytic sources of the luminescences are discussed.