PHOTOCHROMIC SYNERGISM OF BACTERIORHODOPSIN- and HALORHODOPSIN-MEDIATED PHOTOPHOSPHORYLATION IN Halobacterium halobium*

Quantitative action spectroscopy was performed in Halobacterium halobium. using four suited pigment mutants, namely the bacteriorhodopsin and halorhodopsin positive mutant strain M-l (BR⁺, HR⁺), the bacteriorhodopsin positive but halorhodopsin negative strain M-18 (BR⁺, HR^-), the bacteriorhodopsin negative but halorhodopsin positive strain L-33 (BR^-, HR⁺), and the bacteriorhodopsin and halorhodopsin negative strain L-07 (BR^-, HR⁺). The approached questions were: First, photoenergetic synergism of halorhodopsin and bacteriorhodopsin in intact cells; second, photochromism and cellular function of the blue light-absorbing intermediates, i.e. M-412 and HR-410 in bacteriorhodopsin and in halorhodopsin, respectively. Dark-adapted cells of mutant strain M-l show wavelength-dependency of quantum yield of photo-phosphorylation, φ_ATP. An 1.4-fold enhancement was found at 575 nm wavelength where the long wavelength absorbance bands of bacteriorhodopsin and halorhodopsin intersect. The enhancement vanished after a 30 min pulse of orange light (600 Wm^-2 bandpass from 495 to 750 nm), but was restored after a 30 min pulse of blue light (100 Wm^-2 bandpass from 325 to 480 nm). Photoreversibility of this enhancement probably reflects phototransformation of halorhodopsin from its ground state into its inactive intermediate, HR-410, and vice versa. The halorhodopsin-mediated enhancement with maximum quantum yield of photophosphorylation, φ_ATP= 0.06, i.e. a quantum requirement of = 17 photons/ATP, is partly substituted by a rise in phosphate potential and explained in terms of a voltage-regulated gating effect on the H⁺-driven ATP-synthase, superimposed on the chemiosmotic mechanism of energy coupling. The blue-absorbing photochromic intermediate, M-412 of bacteriorhodopsin, dissipates light energy upon photoexcitation that is reflected by a spectral decline in quantum yield of photophosphorylation to a minimum value of = 0.01 at 415 nm, i.e. a quantum requirement of = 100 photons/ATP.     

THE WHITE MEMBRANE OF CRYSTALLINE BACTERIOOPSIN IN HALOBACTERIUM HALOBIUM STRAIN R1mW AND ITS CONVERSION INTO PURPLE MEMBRANE BY EXOGENOUS RETINAL

Abstract— A new strain isolated from Halobacterium halobium designated R₁mW, contained negligible amounts of isoprenoid pigments, had a yellowish white color due to respiratory pigments and showed no proton movement in response to light. However, addition of all-trans-retinal converted R₁mW into purple cells. Formation of both halorhodopsin and bacteriorhodopsin was indicated by induction of light-dependent proton uptake and release, respectively. Both haloopsin and bacterioopsin were thus postulated to be present in R₁mW. Electron micrographs of freeze-fractured cytoplasmic membranes revealed patches in a hexagonal array of trimeric particles, comparable to the purple membrane structure. These white membrane patches were isolated by procedures similar to those for the purple membrane. The white membrane's buoyant density was about 1.18 g/m/, and its main component migrated on sodium dodecylsulfate polyacrylamide gels at the same rate as bacteriorhodopsin. The white membrane showed only a small absorption peak at ～410nm due to contaminating respiratory pigments and a strong absorption at around 275 nm and shorter wavelengths. The white membrane was thus considered to be mainly composed of bacterioopsin, which was readily converted into bacteriorhodopsin by an addition of all-trans-retinal. The absorption and CD spectra of the white membrane were measured before and after addition of retinal. The molar extinction coefficient of dark-adapted bacteriorhodopsin formed was determined to be 53000M^?1 cm^?1 at 560 nm from retinal binding studies. The CD spectrum of the white membrane was negligible in the visible region but showed several bands assigned to aromatic and backbone structures in the UV region. Retinal addition caused considerable changes in the spectrum, yielding the CD spectrum of crystalline purple membrane bacteriorhodopsin. The white membrane thus appears to be a preparation suitable for structure-function studies of bacteriorhodopsin.     

Monitoring of Solar Irradiance in the High Andes

Solar radiation has been measured in the high Andes near Laguna Lejia (latitude 23° 26′ 23.30" S, longitude 67° 38′ 14.29" W) at an elevation of 4715 m between December 2016 and December 2017. Irradiances were monitored in four wavelength channels: PAR (400–700 nm), UV-A (315–400 nm), UV-B (295–315 nm) and short-wavelength UV-B (295–310 nm) with a new radiometer. In addition, ambient temperatures were recorded. Record values have been found for PAR (exceeding 600 W m⁻²), UV-A (close to 95 W m⁻²), UV-B (3.13 W m⁻²) and short-wavelength UV-B (0.144 W m⁻²) during Austral spring. The winter irradiance values slightly exceeded 50% of these values. Maximal cloud effects due to multiple reflections were 45, 38, 32 and 35% higher than values under cloudless skies for PAR, UV-A, UV-B and short-wavelength UV-B, respectively. Record irradiance for this site shows a UV index reaching and exceeding 20, which is due to low solar zenith angles, the altitude, low water vapor and aerosol concentrations in the atmosphere as well as low total column ozone concentrations.     

Photochemical reactions of radical cations of dimethylformamide in freon matrices at 77 K

Spectral characteristics of the radical cations (RC) of DMF (λ_max = 415 nm, ε_max = (2.6±0.8)·10³ L mol^?2 cm^?2) stabilized in an irradiated glassy freon mixture (CFCl₃ and CF₂BrCF₂Br) at 77 K were determined. Amide type radicals and RC of the matrix were shown to be formed by irradiation (λ=365–436 nm) of the radical cations of DMF in freon matrices using ESR and UV spectroscopy. The quantum yields of photoconversion of the DMF radical cations are independent of the wavelength of exciting light. It was found that the matrix structure affects the processes stabilizing the products of photoconversion of the DMF radical cations.     

The kinetics and mechanism of n-butyraldehyde photolysis in the vapor phase at 313 nm

The photolysis was investigated at 313 nm wavelength, 253–529 K temperatures, and 4 × 10^?11-2 × 10^?9 mol·photon/cm²·sec light intensities by determining the quantum yields of 20 reaction products. Primary quantum yields for the seven primary processes and rate constant ratios, rate constants, and Arrhenius parameters for secondary processes were derived on the basis of the suggested reaction scheme. The dependence of the quantum yields of the four major primary processes on experimental conditions was established.     

POTENTIAL ERRORS IN THE USE OF CELLULOSE DIACETATE AND MYLAR FILTERS IN UV-B RADIATION STUDIES

Abstract— The increase in UV-B radiation(290–320 nm) penetrating to the earth's surface as a result of the chemical depletion of the stratospheric ozone layer is an important environmental concern. In most studies using artificial UV-B sources, the determination of enhanced UV-B radiation effects on plants relies on equivalent UV-A radiation(320–400 nm) from the experimental UV-B fluorescent lamp source, filtered with either cellulose diacetate (CA) to create UV-B treatments, or with type S Mylar or polyester (PE) to create controls (no UV-B). The spectral irradiance in the UV-A was measured in the dark below lamps at two daily UV-B irradiance levels (14.1 and 10.7 W m^-2) with CA and PE at two ages. Highly significant differences in UV-A radiation (P 0.01) were measured below the treatment/control pairs at both fluence rates and filter ages. Filter aging was observed, which reduced the UV-A irradiance, especially for PE. The total daily ambient UV-A irradiance was also determined in the glasshouse at three seasons: the fall equinox, summer and winter, from which the total daily UV-A (lamp + ambient) irradiances were calculated. The addition of low to moderate ambient irradiance removed the treatment/control differences in the longwave UV-A(350–400 nm); however, the treatment/contro1 differences remained in the shortwave UV-A(320–350 nm), which was restricted by the glass, and in the total UV-A. The treatment/control differences persisted in the shortwave UV-A for the higher irradiance level, even under high summer ambient light. Also, spectral ratios (UVB:UV-A and shortwave: longwave UV-A) for all treatment groups decreased as the ambient UV-A radiation increased. Therefore, a range of experimental conditions exist where PE-covered lamps do not provide adequate control for UV-A irradiance, relative to the CA treatment, for glasshouse/growth chamber experiments. Potential complications in the interpretation of plant response exist for UV-B experiments conducted under low ambient light conditions (e.g. growth chambers; glasshouse in winter) or high daily UV-B irradiances (e.g. 14 kJ m^-2) for those plant responses that are sensitive to UV-A radiation.     

A ROLE FOR MENADIONE IN THE PURPLE MEMBRANE PROTON PUMP?

Abstract— It has been assumed that proton pumps such as purple membrane lack redox loops. However, purple membrane does contain an electron carrier. Kates et al. (Meth. Enzymol. 88,98–1 111, 1982) reported the presence of 1 mole of vitaminMK–8 to 6 mol of bacteriorhodopsin among the nonpolar lipids. Is this quinone functionally important in the proton pump mechanism? Proton pumping rates were measured with lipid-free bacteriorhodopsin reconstituted in vesicles to which varying amounts of vitamin K₁ were added. With soybean lipids, in the presence of tetraphenyl boron, the pump quantum yield was 0.04H⁺/photon. This result was independent of the amount of vitamin K, added over a range of 0 to a 100-fold mole ratio to bacteriorhodopsin. A similar result was obtained with H. halobium lipids. The pump quantum yield in vesicles is much less than reported for membrane sheets and whole cells. The results support the conclusion that a vitamin K Q-cycle is not involved in the purple membrane proton pump.     

LOW TEMPERATURE ABSORBANCE AND FLUORESCENCE SPECTROSCOPY OF THE PHOTOACTIVE YELLOW PROTEIN FROM Ectothiorhodospira halophila

A simplified procedure was developed to purify the photoactive yellow protein (PYP) from Ecrorhiorhodospira halophila. Specific antibodies were used to follow the distribution of PYP through the separate purification steps. Low temperature absorbance and fluorescence characteristics of this photoactive protein were investigated. The absorbance spectrum of PYP in 67% (vol/vol) glycerol peaked at 449 and 447 nm, at room-and liquid nitrogen temperatures, respectively. It sharpened significantly upon cooling to 77 K and displayed fine-structure on the blue side of its absorbance maximum, with a spacing of 25 nm. At room temperature PYP fluoresced with a quantum yield of approximately 3.5 times 10^?-³ an emission maximum of 495 nm. Maximal excitation occurred at 457 nm, 10 nm red-shifted with respect to the absorbance maximum. At -low temperature the excitation maximum remained unaltered but maximal emission shifted significantly to the blue (to 482 nm). The quantum yield of fluorescence increased to 0.07 at this temperature. Illumination of PYP at low temperature with light from the visible part of the spectrum of electromagnetic radiation induced pronounced changes in its absorbance and fluorescence characteristics. At least two new stable intermediates were formed: one highly fluorescent, with an excitation maximum at 430 nm; additionally, a non-fluorescent red-shifted intermediate with an absorbance maximum at 490 nm. The amount formed of these two intermediates depended strongly on the wavelength of actinic illumination. In combination, these data underline the spectroscopic similarities between PYP and the retinal-containing chromoproteins that are present in Halobacterium halobium.     

UV Absorptance of Titanium Dioxide Thin Films by Plasma Enhanced Deposition from Mixtures of Oxygen and Titanium-Tetrakis-Isopropoxide

A low pressure radio frequency discharge was used to deposit films by mixtures of oxygen and titanium (IV) isopropoxide (TTIP) at powers of 200 W on films of polyethylene-terephthalat and samples of quartz glass. In the non-thermal plasma, films of rather pure TiO₂ could be deposited as revealed by X-ray photo-electron spectroscopy. Besides the film growth rate and the chemical composition, the spectral behaviour of the spectral transmittance of visually transparent films was determined in the range from 200 to 500 nm. Furthermore, the absorptance of films has been derived at characteristic spectral positions of the transmission spectra of the films. Accordingly, cut-off wavelength was found to increase with deposition time from 5 to 10 min as well as with the concentration of TTIP in a range below 1.7%. At 310 nm, the spectral absorption coefficient (extinction coefficient × concentration) was 12 μm⁻¹. While keeping other parameters constant, this coefficient decreased by 4 μm⁻¹ due to an increase of the concentration of TTIP from 1.7% to 8%. Simultaneously, the surface roughness increased as revealed by profilometry. Thus, since the chemical structure of films was found to change only marginally, a decrease of the film density is likely to cause the observed dependence of the absorption coefficient with increasing precursor concentration.     

UV-assisted degradation of propiconazole in a TiO2 aqueous suspension: identification of transformation products and the reaction pathway using GC/MS

Photocatalytic degradation of propiconazole, a triazole pesticide, in the presence of titanium dioxide (TiO₂) under ultraviolet (UV) illumination was performed in a batch type photocatalytic reactor. A full factorial experimental design technique was used to study the main effects and the interaction effects between operational parameters in the photocatalytic degradation of propiconazole in a batch photo-reactor using the TiO₂ aqueous suspension. The effects of catalyst concentration (0.15–0.4 gL^?1), initial pH (3–9), initial concentration (5–35 mg L^?1) and light conditions were optimised at a reaction time duration of 90 min by keeping area/volume ratio constant at 0.919 cm² mL^?1. Photocatalytic oxidation of propiconazole showed 85% degradation and 76.57% mineralisation under UV light (365 nm/30 Wm^?2) at pH 6.5, initial concentration 25 mg L^?1 and constant temperature (25 ± 1 °C). The Langmuir–Hinshelwood kinetic model has successfully elucidated the effects of the initial concentration on the degradation of propiconazole and the data obtained are consistent with the available kinetic parameters. The photocatalytic transformation products of propiconazole were identified by using gas chromatography–mass spectrometry (GC/MS). The pathway of degradation obtained from mass spectral analysis shows the breakdown of transformation products into smaller hydrocarbons (m/z 28 and 39).     

A NEW DOSIMETER FOR ULTRAVIOLET-B RADIATION

Abstract— A type of polycarbonate plastic was found to be sensitive to ultraviolet (UV) radiation. The damage to the material due to UV exposure was revealed by etching in a strong alkaline solution. The latent effect can be retained in the material for a period of at least 30 days. The material was tested for use as a detector of ultraviolet-B (UV-B 280–320 nm) radiation.
The response of the detector in the wavelength region between 254 and 365 nm was determined using a set of narrow-band filters and a 200 W UV xenon-mercury lamp. The maximum UV effect in the detector was observed at a wavelength of 290 nm. The spectral response curve was found to be similar to the human erythema action spectrum.
The detector may be miniaturized for dosimetric applications. The dose response curve is linear in the region up to an erythemal dose of 300 mJcm⁻². Laboratory and field tests showed that the dosimeter response to UV exposure was additive and was independent of dose rate. Further experiments suggested that the dosimeter was stable against changes in temperature and humidity.     

ARE THERE SEVERAL PHOTORECEPTORS INVOLVED IN PHOTOTROPISM OF Phycomyces blakesleeunus? KINETIC STUDIES OF DICHROMATIC IRRADIATION*

Abstract— Photogeotropic equilibrium angles were measured for Phycomyces blakesleeanus wild type firstly by means of dichromatic fluence rate response curves using simultaneous irradiation with near threshold 450 nm reference light (constant at 1.2 × 10^?8 W m^?2) and variable fluence rates of test light (498–630 nm) from the same side. These curves showed minima for test light fluence rates that were close to the photogeotropic threshold for these wavelengths. Secondly, the time course of this inhibitory effect was studied with both the inductive reference 450 nm light (2 × 10^?-⁷ W m^?2) and the test light (606 or 450 nm) given as light pulses of 2 s duration (2 s light/48 s dark periods for 6 h). The dark period between the onset of the inductive reference light and test light pulses was varied between 0 and 48 s. No inhibitory effects were observed for simultaneous pulses; however, inhibitory effects were demonstrated for delay times of 2 s and 20 s for 606 nm as well as 450 nm test light. If the test light pulses were given immediately before the inductive reference light, only 606 nm test light was effective in producing a significant inhibitory effect. The results are discussed with regard to a multichromophoric photoreceptor system and to the wavelength dependence of the effects observed. The data and conclusions favor a photoreceptor system with at least two separate chromophoric absorptions of the blue light receptor type, one acting positively, the other acting inhibitorily, and at least one other photoreceptor of presumably minor influence.     

The Rules Governing the Formation of Silver Azide Photolysis Products

Irradiation of silver azide at λ = 365 nm (I > 1 × 10¹⁵ quantum cm^?2 s^?1) in a vacuum (1 × 10^?5 Pa) leads to an increase in the rate of photolysis and photoinduced current and the appearance of a new long-wave region of spectral sensitivity. The photolysis products, silver metal and gaseous nitrogen, are formed in a stoichiometric ratio on the surface of silver azide. The rate constants for silver azide photolysis were determined. Measurements of contact potential difference, current—voltage characteristics, photoelectromotive force, and photocurrent showed that AgN₃(A₁)—Ag (photolysis product) microheterogeneous systems were formed in silver azide photolysis. The limiting stage of silver azide photolysis is the diffusion of interstitial silver cations to the (T_nAg_m)⁰ neutral center.     

Microcalorimetric Studies of the Toxic Action of La^3＋ on Halobacterium Halobium R1 Growth

A microcalorimetric technique was used to evaluate the influence of La^3 on Halobacterium halobium R1 growth.By means of LKB-2277 bioactivity monitor,ampoule methos at 37℃,the thermogenic curves of Halobacterium halobium R1 growth were obtained.In order to analyze the results,the maximum power Pm and the growth rate constants k were determined,showing that values of Pm and k are linked to the concentration of La^3 .Addition of low concentration of La^3 can cause a decrease of the maximum heat production and growth rate constant.However,high concentration of La^3 may promote growth of Halobacterium halobium R1,but at much higher concentration of La^3 ,the growth of Halobacterium halobium R1 is inhibited again.For comparison,the shapes of Halobacterium halobium R1 cell were observed by means of transmission electron microscope.According to the thermogenic curves and TEM photos of Halobacterium halobium R1 under different conditions,it is clear that metabolic mechanism of Halobacterium halobium R1 growth is changed with the addition of La^3 .     

Photochemical reactions of bis(η5-cyclopentadienyl)- titanium dichloride

Irradiation of benzene solutions 10^?3M in both titanocene-d₁₀ dichloride and titanocene dichloride with light of wavelengths 313, 360, 400, and 520 nm leads to the formation of titanocene-d₅ dichloride with quantum yields of 0.02, 0.005, 0.01 and 0.007 mol Ei^?1, respectively. Photodecomposition of titanocene dichloride is negligible even at much longer photolysis times than those required for isotopic equilibration. Photolysis of benzene solutions 10^?2M in titanocene dichloride and 1.0 M in methanol leads to the formation of cyclopentadienyl(methoxo)titanium dichloride with a quantum yield of about 0.08 mol Ei^?1 when the irradiating wavelength is 313 nm.     

Synthesis,structure, and optical properties of an alternating calix[4]arene‐based meta‐linked phenylene ethynylene copolymer

Novel alternating copolymers comprising bis‐ calix[4]arene‐p‐phenylene ethynylene and m‐phenylene ethynylene units ( CALIX‐m‐PPE ) were synthesized using the Sonogashira‐Hagihara cross‐coupling polymerization. Good isolated yields (60–80%) were achieved for the polymers that show M_n ranging from 1.4 × 10⁴ to 5.1 × 10⁴ gmol^?1 (gel permeation chromatography analysis), depending on specific polymerization conditions. The structural analysis of CALIX‐m‐PPE was performed by ¹H, ¹³C, ¹³C–¹H heteronuclear single quantum correlation (HSQC), ¹³C–¹H heteronuclear multiple bond correlation (HMBC), correlation spectroscopy (COSY), and nuclear overhauser effect spectroscopy (NOESY) in addition to Fourier transform‐Infrared spectroscopy and microanalysis allowing its full characterization. Depending on the reaction setup, variable amounts (16–45%) of diyne units were found in polymers although their photophysical properties are essentially the same. It is demonstrated that CALIX‐m‐PPE does not form ground‐ or excited‐state interchain interactions owing to the highly crowded environment of the main‐chain imparted by both calix[4]arene side units which behave as insulators inhibiting main‐chain π–π staking. It was also found that the luminescent properties of CALIX‐m‐PPE are markedly different from those of an all‐p‐linked phenylene ethynylene copolymer ( CALIX‐p‐PPE ) previously reported. The unexpected appearance of a low‐energy emission band at 426 nm, in addition to the locally excited‐state emission (365 nm), together with a quite low fluorescence quantum yield (? = 0.02) and a double‐exponential decay dynamics led to the formulation of an intramolecular exciplex as the new emissive species. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

STEADY HYPSOCHROMIC SHIFT OF PEAK RESPONSIVITY TO ATTRACTANT LIGHT FROM 590 nm TO 560 nm IN Halobacterium halobium*

Abstract— Peak responsivity of photoattraction in Halobacterium halobium cells shows steady hypsochromic shift from 590 nm wavelength under low irradiance conditions to 560 nm under high irradiance conditions. Inversion of the photoattractant response, as dependent on blue vs red background light, is compatible with the known properties of photochromic sensory rhodopsin-I (SR-I) with ground state maximum absorption at 587 nm. Relaxation of the photoattractant response in H. halobium, as a function of wavelength and irradiance, gives a hint at an antagonistic pigment or intermediate state, different from ground state SR-I, with peak sensitivity at 620 nm or even above. The less sensitive photoattractant response at 560 nm persists without photorelaxation and represents the peak responsivity under high irradiance conditions.     

REVERSIBLE PHOTOCYCLOADDITION OF A 4',5'-DIHYDROPSORALEN DERIVATIVE WITH THYMINE

The photocycloaddition reaction between a 4′,5′-dihydropsoralen derivative and thymine was studied in solution using a synthetic bichromophoric model 8 in which the two rings are associated by a tetramethylene chain. In water this model molecule exhibits intramolecular ring-ring stacking interactions as evidenced by UV and NMR spectroscopies. Irradiation at 365 nm at usual concentrations ( 5.10^?-⁴M) leads exclusively to a regio- and stereo-selective dimerization reaction involving the 3,4 double bonds of the psoralen moities. Extreme dilutions (ca 2.10^?-⁵M) were necessary to observe the intramolecular reaction which results in the exclusive formation of a 3,4 cb-anti adduct. This reaction is completely reversed by irradiation at 254 nm. These results are discussed with regard to the behavior of the homologous models in which the furan part of the psoralen ring is not hydrogenated, These latter compounds also lead exclusively to a 3,4 cis-anti adduct. It appears that saturation of the furan ring increases strongly the quantum yield of the photaddition at 365 nm (0.01 → 0.18) and that the triplet excited state of the 4′,5′-dihydropsoralen is involved in the photoaddition.     

Photodegradation of polyacetaldehyde in solution. I. Direct photolysis

The quantum yields measured for the random scission of main-chain bonds of polyacetaldehyde in benzene solution by 254 nm irradiation at 298°K are on the order of 10^?3–10^?4 scissions per quantum absorbed by the polymer. The quantum yields are unaffected by oxygen but are dependent upon initial polymer concentration and upon the inverse square root of absorbed light intensity. The direct photochemistry involves excitation of carbonyl chromophores in their ¹nπ^* bands, and a Norrish type I process is believed to be responsible for subsequent free-radical random-chain scissions. It has been established that direct photoexcitation processes do not lead to sequential depolymerization of polyacetaldehyde to monomer.     

DO PYRIMIDINE DIMER YIELDS CORRELATE WITH ERYTHEMA INDUCTION IN HUMAN SKIN IRRADIATED in situ WITH ULTRAVIOLET LIGHT (275–365 nm)?

Ultraviolet radiation produces erythema in human skin, and damages the DNA of living cells in skin. Previous work showed that broad-band UV-B (290-320 nm) radiation produced higher levels of cyclobutyl pyrimidine dimers in DNA of individuals with high UV-B sensitivity (low minimal erythema dose) than in subjects of low UV-B sensitivity [Freeman et al. (1986) J. Invest. Dermatol., 86, 34-36]. We examined the relationship between erythema induction and dimer yields in DNA of human skin irradiated in situ with narrow band radiation spanning the wavelength range 275-365 nm. We find that, in general, higher dimer yields are produced per incident photon in volunteers with higher susceptibility to erythema induced by radiation of the same wavelength.