摘要:

Abstract—A striking increase in the shoulder of the u.v. survival curve but no change in the limiting slope is obtained when cultures ofEscherichia colistrain TAU complete the DNA replication cycle in the absence of concommitant protein synthesis prior to irradiation. The u.v. sensitivity of protein synthesis or RNA synthesis is not altered significantly by this treatment.In contrast to the result for strain TAU, there is no significant change in the u.v. survival curve for the u.v. sensitiveE. coliBs‐1when its DNA replication cycle is completed under similar conditions.Following a period of inhibited protein synthesis there is a delay in the reinitiation of the normal DNA replication cycle when protein synthesis resumes. This delay would allow time for an intracellular repair system to operate before the attempted resumption of normal replication. Strain Bs‐1, which is deficient in this repair system, would not be expected to benefit from such a delay, as consistent with the observed results. A model is presented to account for lethality due to attempted DNA replication during a period of repair synthesis. Themaximumsurvival for a given u.v. dose would be predicted for a culture which has completed the normal DNA replication cycle prior to irradiation and which is not permitted to reinitiate the cycle until all possible repair synthesis is comp

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05756.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Studies of purine absorption and emission in seven solvents differing greatly in dielectric constant and hydrogen bonding potential, reveal a variety of solvent effects. For example, the resolution of structure in the absorption spectrum, the position and/or intensity of the X2absorption band, the intensity of fluorescence, the magnitude of the long wave‐lenth tail, and the position of the X1absorption band are differentially affected—in the order listed—by the solvents tested. Even though it is possible to correlate the extent of decrease in then‐π*tail with increasing solvent dielectric constant, probably alterations in all of these spectroscopic parameters depend most critically upon the ability of the various solvents to form hydrogen bonds with the hydrogen on N9 and/for with the non‐bonding electrons on the purine nitrogens: it is tentatively concluded that the probability of hydrogen bonding is directly correlated with the electronegativity of the aza nitrogens (N7>N3>N1). In solvents like isopropanol not all of the non‐bonding electrons must be solvated maximally in most purine molecules since there is appreciable fluorescence under conditions where a long wavelength tail is readily observed in the absorption spectrum (alternatively some noa‐bonding electrons may not te relevant to fluorescence quenching.) Decreases in fluorescence yield are associated with red shifts in the fluorescence maximum, and in the solvents of highest polarity the fluorescence yield is again small indicating that glycerol and water can enhance radiationless tunneling—presumably by altering Franck‐Condon configurations and/or improving electronic‐vibrational coupling between solute and solvent. The quantum yield is uniform throughout the atsorption band for a given solvent, but studies in aqueous buffers varying from pH 1 to 11 show that the fluorescence yield is greater for charged than for neutral molecules. Further, the fluorescence excitation peak is red shifted in powders. Since phosphorescence is the predominant emission at 777deg;K and increases in fluorescence can be correlated with the presumed solvation of non‐bonding electrons, the singlet excited state of lowest energy in ‘unperturbed’ purine must ben‐π*in nature. The shape of the phosphorescence band and the decay lifetime of ˜ 1 sec at 77°K lead to the conclusion that the emitting triplet is aπ‐π*state. The eight vibrational structures in phosphorescence emission can be readily grouped into two progressions: there is an average separation of about 1300 cm‐1between peaks within a given progression, and the two sets are mutually displaced by about 500 cm‐l. Individual vibrational peaks are favoured in different solvents and the whole band may be shifted up to 500 cm‐l. Even larger shifts are observed in charged purine molecules and in powders (up to 3000 cm

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05757.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Young sporangiophores of the fungus,Pilobolus kleinii, respond to unilateral illumination by bending or by growing toward light of wavelengths between 312 and 530 mμ, with peaks of sensitivity near 360 and 450 mμ. Young sporangiophores exhibit a negative phototropic response to wavelengths shorter than 300 mμ, with a strong negative response at 280 mμ. Since the action spectrum did not correspond to the absorption spectrum of the pigmented zone as measuredin vivo, and since colorless sporangiophores formed on media containing diphenylamine were capable of phototropic response, it is unlikely that the conspicuous orange‐yellow pigment in young sporangiophores is the photoreceptor for phototropism. The results of probing with small beams of light and the behavior of sporangiophores submerged in mineral oil, together with measurements of the refractive index of the tip and base indicate that the photosensitive region is located in the tip of the young sporang

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05758.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—The absorption and fluorescence spectra of riboflavin, riboflavin tetrabutyrate and lumichrome have been studied in organic solvents of different polarity including ethanol, acetone, dioxane, pyridine, acetic acid and in cyclohexane‐dioxane mixtures. The molar extinction coefficients of the compounds were measured and the character of solvent sensitive changes observed in the absorption spectra are discussed. The effect of hydrogen bonding and/or intramolecular charge transfer complex are proposed as possible explanation.Changes in the shape of fluorescence emission spectra are less evident; in the case of riboflavin tetrabutyrate, mirror symmetry to the shape of the longest wavelength maximum was observed in low‐polar solvents. Quantum yields of fluorescence are higher the lower the polarity of the solvent used; the value for riboflavin tetrabutyrate is greater than for riboflavin. Changes were also observed in the fluorescence emission spectra of lumichrome in solvents of different polarity.Fairly good agreement was demonstrated for positions of the observed absorption maxima of riboflavin in 98% dioxane, riboflavin tetrabutyrate and lumichrome in 80% cyclohexane in mixture with dioxane and the values calculated from energies of molecular orbitals of flavins computed by B. Pullman and A. Pu

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05759.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—The photodegradation of riboflavin by 436 mμ monochromatic light and of lumichrome by white nonfiltered light was studied in a set of organic solvents including ethanol, acetone, dioxane, pyridine and acetic acid. For comparison, water was used as a solvent. Photolysis was carried out in the presence of atmospheric oxygen.Riboflavin and lumichrome were found to be effectively stabilized towards the action of light by hydrogen bonds with solvent molecules, and consequently are most light‐stable in water solutions. The overall scheme of riboflavin photolysis in organic solvents seems to be the same as in aqueous solutions. Lumichrome has been found as the main product of riboflavin photolysis in the organic solvents te

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05760.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—The phenomenon of gamma ray thermoluminescence has been studied in DNA, RNA, and their various constituents. Single peaks in the glow curves have been usually observed at 110–120°K except in cytosine which shows two peaks at 135°K and 180°K. Adenine and cytosine show very intense thermoluminescence whereas the intensity of light emitted from thymine, uracil and guanine is very small. The addition of sugar and sugar‐phosphate groups to the base‐molecules affects only the amount of light emitted. The thermoluminescence emission spectra lie in the same wavelength region as the u.v. induced phosphorescence, suggesting a triplet‐singlet transition. The spectral content of DNA thermoluminescence seems to be superposition of contributions from its constituents. An attempt is made to explain the phenomenon as a result of electron‐cation

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05761.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Far‐red light has the property of promoting the elongation ofAvenamesocotyl sections in the presence of a gibberellin. Part of this effect is not reversible by red light (around 655mμ). The wavelengths which are most effective are those in the neignbourhood of 720mμ, as revealed by the action spectrum. Amongst the 8 gibberellins tested, only A1, A3, and A9, are capable of producing, after far‐red irradiation, a greater elongation than the one they cause in t

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05762.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Substitution of an amino group at the C2 carbon of purine causes the two main components of the X absorption band to be separated by 200–500 Å: primarily this reflects the Occurrence of the lowest‐lying transition at much longer wavelengths than in purine since, except in deoxyguanosine, there is an appreciable absorption component at ˜ 2420 Å in these compounds. Unlike purine, the wavelength shifts produced by different solvents are not simply related to the dielectric constant or hydrogen bonding capacity of the solvents. In agreement with previous predictions thatπ‐π*states should be the lowest‐lying excited singlets, no phosphorescence is observed from 2–aminopurine—the fluorescence quantum yield is close to unity. Besides strong fluorescence very weak phosphoresence can be detected when another amino group is added at C6 and when an oxygen is attached to the sixth carbon (guanine) fluorescence and phosphorescence of comparable intensities are observed: the sum of the quantum yields for both types of emission is of the order of unity. Thus, the lowest‐lying singlet transition must be aπ‐π*state. At room temperature themal quenching is the most important parameter in determining the fluorescence intensity of these molecules, however, at lower temperatures the intensity—similar to the wavelength—f this emission apparently also depends upon the ability of a given solvent to reorient and/or perturb Franck‐Condon surfaces. Discrepancies observed between absorption and excitation spectra in deoxyguanosine and azaguanine appear to reflect emission caused respectively by aggregation of mol

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05763.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—The ocellar pigment ofSpirocodon saltatrixwas extracted with 2% mildly alkaline cetyltrimethylammonium bromide (CTAB) and 90% methanol acidified with HCl. In the case of CTAB‐extracted pigment, maximum changes in optical density upon illumination occurred in mildly alkaline media under aerobic conditions and in neutral media under anaerobic conditions. The density spectrum of the sample illuminated under anaerobic conditions closely resembled that of the reduced form of the pigment illuminated in the presence of air. When reduced in darkness, the pigment became photostable and its density spectrum differed from that of the pigment reduced after illumination. On aeration of the pigment solution illuminated under anaerobic conditions, its density spectrum in the visible range became similar to that of the pigment illuminated in the presence of air. A trace of air dissolved in experimental media caused auto‐oxidation of the reduced form, during the process of which a definite isosbestic point was observed at 480 mμ. Under anaerobic conditions, short period of illumination produced changes in spectral absorbance only in the visible range. Changes in the u.v. range required longer exposures. The pigment extracted with acidified methanol was readily auto‐oxidizable and it was the reduced form which showed photosensitivity, though the degree of sensitivity was extremely low. The density spectrum of illuminated pigment resembled that of the oxidized form. From these experiments, a tentative scheme involving an electron transfer system has been suggested for the chain of photic reaction of the anthomedusan ocellar

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05764.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Chloroplasts illuminated with light absorbed predominantly by Photosystem I can mediate the photoxidation of ascorbic acid to threonic and oxalic acids. Two micromoles of oxygen are consumed for each micromole of ascorbic acid added. The kinetics of this endogenous chloroplast system closely resemble the kinetics of an artificial flavin‐manganese‐catalase system in which flavin is the photosensitizin

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05765.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY