摘要:

Abstract—Photosynthetic reaction centers isolated from blue‐green mutant strain R‐26 ofRhodopseudomonas spheroideswere used to study the action spectra for the light‐induced absorption changes at 880 nm, and for the P870 fluorescence. These spectra indicated that a pigment, possibly bacteriopheophytin, with an absorption maximum at 757 nm is an intrinsic component of the reaction center and transfers energy to P870 with relatively high eff

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06186.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Acid‐base, acid‐, and salt‐induced chemiluminescences of chloroplasts were investigated in relation to their dependences upon several time parameters:1The dependence of the three chemiluminescences on the preillumination time was similar; the luminescences rose to a maximum and then decayed to a steady‐state This behaviour depends on the preillumination level and the length of the dark time following the preillumination. Analysis of the above indicates the formation of quenching entities during the preillumination which react with the luminescence precursors mainly in the dark.In contrast, the delayed light measured after 22 msec from the preillumination, showed a much slower but smooth rise to the steady‐state with no subsequent drop.2During the dark period following preillumination the ability of the system to chemi‐luminescence decayed with a first order rate.3During emission the above chemiluminescences decayed with a first order law. The total emission in different experiments was also proportional to the maximum emission, in agreement with a first order law of decay.4The comparison of the kinetic behaviour of the three types of chemiluminescence indicates common precursors of luminescence for at least the acid‐base and the salt types. The delayed emission at 22 msec however, seems to have separate precursors than the three che

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06187.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—The influence of nutrition on the sensitivity ofEscherichia coli15T‐to ultraviolet light (u.v.) and the synthesis of DNA has been studied. Growth in media containing glucose or NH,+has been found to endow cells with a greater resistance to lethal u.v. damage than those grown in media containing succinate or amino acids, respectively. In addition, the sensitivity of the lactose (lac) locus of the DNA to mutagenic damage has been found to be altered by changes in the carbon supply but not by changes in the nitrogen source, while the sensitivity of loci controlling amino acid synthesis was altered by changes in the nitrogen source but not in the carbon source. Cells fed with glucose or NH4+have been found to possess more DNA than cells fed with succinate or amino acids, respectively. The data indicate that the type of carbon and nitrogen supplied to the cells will determine whether or not set regions of the DNA will undergo more than one round of replication. The presence in the cell of identical genetic loci either in duplicate or in multiples, directed by the particular types of carbon and nitrogen supplied, is suggested to be, in part, the reason why an alteration in nutrition is able to influence the sensitivity of bacterial cells to radiat

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06188.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—The applicability of Stepanov's relation to solutions of chlorophyllain 17 solvents was determined. The value ofT*(the local temperature of the excited molecules calculated by the relation) was higher thanT(the ambient temperature) in 7 solvents and lower in one. The relative quantum yield determined by comparing the fluorescence spectrum with the thermal emission spectrum was fairly constant (˜ 1.0) up to 690 nm in dioxane, methylene chloride and dimethylformamide. In other solvents its value at 690 nm varied between 0.2 and 067. It is suggested that existence of a solute‐solute or solute‐solvent interaction in some solvents could possibly cause such a drop in the quantum

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06189.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Two types of photoreactions occur in DNA irradiated in aqueous systems with longwave u.v.‐light (Λ>295 nm), namely, (a) thymine dimerization, and (b) single‐ and double‐strand breakage of the sugar phosphate backbone; these two reactions are unrelated. The presence of acetophenone as a photosensitizer caused an increase in dimerization by a factor of 16, and an increase in single‐strand breaks by a factor of 4. The number of thymine dimers per single‐strand break is about 100 in the sensitized and 25 in the unsensitized reaction. The alteration of the radius of gyration of DNA molecules is that expected by the degradation observed. At the same time the change in hyperchromicity is very small. Therefore as far as can be detected by these methods of investigation the gross conformation of the DNA double helix is stable against thymine

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06190.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—The lowest excited singlet and triplet states of coumarin, psoralen, and 4‐hydroxy‐coumarin have been assigned to the (π,π*) type on the basis of the luminescence spectroscopy and MO calculations. The mechanism of photocycloaddition of courmarin and psoralen to thymine has been described in terms of the perturbational MO model and MO reactivity indices. All possible cycloaddition patterns have been examined. Results suggest that the 3,4‐bond of coumarin in the excited state is somewhat more reactive than the same bond of psoralen in the excited state. It is also predicted that the 3,4‐bond of psoralen in the triplet state is more reactive than the 4′, 5′‐bond. The results have been favorably correlated with the electronic characteristics of excited coumarin molecules and with available experimental data on the relative yield

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06191.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Low temperature techniques are used to record spectra of long wavelength absorbing electrochromic species formed from retinol and related compounds. Formation of these electrochromic species is induced either by iodine or trichloroacetic acid which merely act as acids. The electrochromic species are the corresponding carbonium ions of the respective polyenes. The resulting carbonium ions of a given polyene are identical regardless of whether they are formed by iodine or trichloroacetic acid. The molecular structures of the carbonium ions can be written with certainty. Consequently, the exact nature of the π‐electron system in the polyene and its carbonium ion may be elucid

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06192.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Aggregation of fluorescein, eosin and rose bengal in aqueous solutions has been studied. Mathematical expressions are derived to calculate the monomer mole fractions in moderately and highly concentrated solutions. The average values of the dimer dissociation constant,Kd, for fluorescein, eosin and rose bengal in aqueous solutions at pH 12 are 0.20, 9.0×10‐3and 40 × 10‐3moles/l respectively. A method is developed here to isolate the dimer spectrum from the composite spectrum. The uniqueness of this method is established by comparison with other known methods. The dimer spectra of all the three dyes are r

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06193.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Quantum yields for the formation of the major photoproduct of 2‐14C‐5‐bromo‐2′‐deoxyuridylyl‐(3‘→5’)‐thymidine (BrdUpT) have been determined by irradiation of the 2‐14C‐BrU‐labeled dinucleotide at pH 2.3, 5.9, 7.05, 8.0 and 10.25 with U.V. light at 280nm. At acidic and neutral pH the quantum yield was 0.0063; the value decreased markedly above pH 8.0 to 0.0025 at pH 10.25. Some evidence of the formation of additional photoproducts at high and low pH was found. Some aspects of the mechanism of the reaction are discussed.Consideration of pKavalues calculated for singlet and triplet excited states indicates that the decrease in the quantum yield of main photoproduct at high pH is due to dissociation of the excited bromodeoxyuridine moiety. It is suggested that the formation of BrdUpT photoproduct and the debromination of bromouracil‐labeled DN A occ

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06194.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06195.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY