摘要:

Abstract—Escherichia colicells treated with sublethal doses of acridine plus near‐UV light exhibit an effective split‐dose recovery response that requires an incubation period of about 30–45 min. Studies of the metabolic requirements for split‐dose recovery revealed the following: (a) DNA synthesis is not required for split‐dose recovery; (b) inhibition of electron transport or protein synthesis reduces the efficiency of split‐dose recovery by about one‐half; (c) inhibition of phospholipid synthesis or cell wall synthesis completely eliminates the split‐dose recovery response. These results suggest an involvement of membrane repair mechanisms in response to damage by acridine plus near‐UV light. Additional evidence for such a process was provided by more direct assays for membrane recovery. It was found that cells treated with sublethal doses of acridine plus near‐UV light are sensitive to low concentrations of detergents, and lose that sensitivity upon incubation. Likewise, treated cells are susceptible to lethal osmotic shock, but can recover from this susceptibility if incubated after treatment but prior to exposure to low osmotic conditions. Based on accumulating evidence, we propose thatE. colicells are capable of repairing membrane damage resulting from exposure to acridi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03813.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—The photosensitizing potencies of 5‐methoxypsoraIen and 8‐methoxypsoralen were investigated using the following biological end‐points for lethality: (i) cytolysis in the protozoansParamecium caudatumandTetrahymena pyriformis,(ii) inhibition of growth in the yeastCandida albicansand (iii) survival as measured by colony counts inCandida albicans.In all cases, 5‐methoxypsoralen proved to be the more potent photosensitizing agent. The preliminary action spectra of the 2 compounds for growth inhibition in C.albicanswere similar and showed maximal spectral efficiency in the 320–340 nm waveband. The molecular basis for the described end‐points is unknown. Although it is well known that 5‐methoxypsoralen and 8‐methoxypsoralen readily photoreact with DNA, it is considered that photo‐reaction with protein should also be given serious consideration as the possible lethal event. The superior effect of 5‐methoxypsoralen is in accordance with some of the physical and photochemical properties of this molecule, but this result is at variance with other studies in different test systems that have been used to compare the photobiological efficacy

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03814.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—We present an analytic characterization of upward and downward diffuse spectral irradiance for the wavelength range 280–380 nm, solar zenith angle range from 0 to 86, altitude range from 0 to 5 km and for non‐zero surface albedo. This work is a modification and extension of the previous work of Green, Cross and Smith based upon the radiative transfer calculations of Braslau, Dave and Halpern. Guided by these irradiance systematics we develop an analytic characterization of diffuse spectral scalar irradiance or actinic flux also broken down into upward and downward components for the above wavelengths, solar zenith angles and altitudes, for non‐zero surface albedo utilizing the actinic flux calculations of P

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03815.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—The good transmission of near UV or visible light by human epidermis obtained through mild suction blisters makes it possible to perform quantitative absorption spectroscopy on various photosensitizing dyes such as hematoporphyrin and methylene blue incorporated into the epidermis. The variety of microenvironments found in the skin modifies the photophysical properties of chromo‐phores as shown by optical absorption band red shifts resulting from chromophore‐macromolecule interactions. They also modify the primary photochemical processes as exemplified by measuring the photobleaching quantum yield of the diphenylisobenzofuran, a singlet oxygen probe. The relevance of this study to photomedicine is discussed; in particular, it is shown that some psoralens used in human photochemotherapy can induce photosensitized reactions involving molecular o

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03816.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—The pulsed laser photolysis of light‐adapted bacteriorhodopsin (BR570) is carried out over the temperature range between 25°C and—92°C in neutral and alkaline water‐glycerol solutions. The results arc indicative of considerable complexity, introduced by two temperature dependent branching reactions associated with the intermediates K610, L550and M412, of the BR570photocycle. (a) At relatively low temperatures the primary photoproductK‐610equilibrates with a blue‐shifted species, Kp. Both K610and the new intermediate subsequently decay into another species, K'r, in a process which competes with the formation of L550. Finally, K'pconverts very slowly to L550. This branched pathway delays the formation of L550and thus of M412, without affecting the final yield of either species, (b) A thermal back‐reaction regenerating BR570takes place at the stage of L550, inhibiting the formation of M412. The reaction which also predominates at low temperatures, is relatively inefficient at high pH when the forward L550→ M412step is highly catalyzed. It is the superposition of both branching mechanisms, (a) and (b), which accounts for the complex effects of temperature and pH on the photo‐cycle of BR570. Mechanism (b) is accounted for by a molecular scheme in which deprotonation of a tyrosine moiety at the stage of L550constitutes a prerequisite for deprotonation of the retinal‐lysine schiff‐base as required for forming M412. This scheme appears to be directly related to the proton pump. Mechanism (a) introduces additional complexity in the photocycle at low temperatures but its molecular as

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03817.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—Rate constants for the formation of Pfr, the far‐red‐absorbing form of phytochrome, from photochemical intermediates, have been measuredin vivoin a number of plants. Two first order processes were observed, the slowest of which has been studied in detail. In pea epicotyl hooks, the rate constants proved dependent on temperature as well as on composition of the gas phase. A transition point was observed at about—2°C. Above this temperature the Arrhenius activation energy is 61 ± 6 kJ/mol, below the transition temperature 200 + 17 kJ/mol. The data correspond to half lives of between 0.4 and 0.2 s in an atmosphere of oxygen at 20°C, depending upon the species of plant. In oxygen‐free atmospheres, the rates are between 1.7 and 1.9 times as fast. The data prove that, on the time scale relevant to the usual type of photomorphogenetic experiments, the occurrence of phytochrome intermediates generally can be neglected. Exceptions to this generality are formed by experiments involving continuous or very rapidly intermittent exposures to very high light intensities. Under these conditions the steady state fraction of Pfrmay be considerably lower than calculated from the spectroscopic data for the pigment and the l

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03818.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—The effects of blue light and near UV light on the induction of conidiation in the fungus,Aliernuriu tomato,were investigated. Induction of conidiation was repeatedly controlled by alternating doses of near UV light and blue light. When the final light was near UV, conidiation was induced and conidia developed in the following darkness; when it was blue, the induction of conidiation was suppressed. When conidiation was induced by irradiation with a light mixed with near UV and blue, not only the time lag for inducing conidiation but also the amount of conidia formed were regulated by the fluence rates of both those lights.Thus, ‘mycochrome’ is considered to function as a photoreceptor system in the induction of conidiation of this f

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03819.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—Indole and tetracyanoethylene form a purple charge transfer complex which decomposes into 3‐tricyanovinyI indole and hydrogen cyanide in neutral or basic media. In acid media, 2‐tricyanovinyI indole is formed. 3‐Tricyanovinyl indole has an intense visible absorption at 460 nm, the 2‐isomer is colourless. It is suggested that the visible absorption of 3‐tricyanovinyl indole is due to intramolecular charge transfer and that such a transition is not observed in the case of the 2‐isomer because of a higher excited

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03820.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—Photodestruction of nucleotides by vacuum UV (λ<200 nm) and near UV radiation in thin films has been studied; the products were analyzed by thin‐layer chromatography. Vacuum UV photolysis leads to the rupture of the N‐glycosidic bond with liberation of bases, the quantum yield of the process being about 2 × 10‐4for guanosine‐5'‐monophosphate. No bases have been found among the products of near UV photolysis.Vacuum UV irradiation of aqueous solutions of adenosine‐5'‐monophosphate and guanosine‐5'‐monophosphate produces, along with bases, some other fluorescent substances. The identity of photoproducts of vacuum UV photolysis with those of γ‐radiolysis is established. The mechanism of photochemical

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03821.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY