摘要:

Abstract—The colony‐forming ability ofE. coliBs‐3can be inactivated by light of 313 nm wavelength in an acetone‐sensitized photochemical reaction. This ability can subsequently be restored quantitatively by illumination with photoreactivating light. A small fraction of the population cannot be inactivated; this is assumed to be due to a complete dark repair of the lesions, whatever the dose of radiation has been. Thus, such triplet energy‐transfer experiments can successfully be applied to whole cells. Since thymine dimers are formed almost exclusively, this suggests a new way of studying these lesions in relation to the biologically observabl

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06001.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—Chlorophyll solutions are irreversibly bleached by light in the presence of oxygen. The action spectra parallel the absorption spectra for both chlorophyllaandb.The reaction is of second order with a Q10of 1.26. The reaction rates for chlorophyllsaandbare of the same order of magnitude. Depending upon the light source, the initial rate for chlorophyllais slightly higher, by a factor of 1.15 to 1.30. The rate for pheophytin is lowe 3 by several orders of magnitude. No pheophytin has been detected in the reaction products of the irradiated chlorophyll solutions in the absence of wate

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06002.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—The bleaching of chlorophyll solutions by light in the presence of oxygen can be interrupted, and red intermediates can be precipitated by the use of highly nonpolar solvents in appropriate solvent mixtures. The precipitates are more highly oxygenated but retain phytol and a N‐Mg ratio of 4:1. The NMR spectra indicate that the methine bridge and vinyl protons have been lost. Methyl ethyl maleimide is a product of chromic acid oxidation of the red precipitates. It is also found in the supernatant solution and in the fully bleached end prod

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06003.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—The influence of amino acid prestarvation on both the resistance to u.v. and the postirradiation repair synthesis ofE. coli15 T‐555‐7thy meth arg trpandE. coliB/r (HCR+) was followed. Prestarvation increased the number of survivors about 30–100 fold in both strains at doses 600‐1200ergs/mm2. In contrast to survival no increase in repair synthesis was observed. Thus, the increase in survival has to be brought about by a mechanism which seems to be independent of additional repair

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06004.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—The photovoltaic effect in ethanolic solutions of chlorophyllawith benzoquinone or hydroquinone has been measured as a function of pH. In acidic media, stable, fast‐rising photovoltaic signals of positive sign are obtained. In neutral and basic media, less stable, slower rising photovoltaic signals of negative sign are found. The results in acid media are explained in terms of a photochemical interaction between chlorophyll and either the benzoquinone or hydroquinone producing protons which can then act as the electrode active agent. In basic media, negatively charged radical species, such as the benzoquinone radical‐anion, are considered to be the most likely electrode‐active

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06005.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—Photodimerization of a number of 2,4‐diketopyrimidines including thymine, 1 ‐methylthymine, 3‐methylthymine, 1,3‐dimethylthymine, orotic and 5‐methylorotic acids was studied in the solid state in KBr matrices. A technique developed for quantitative measurements of monomer and dimer concentrations under these conditions by means of u.v. and i.r. spectrophotometry is described. The absorption spectra of crystalline diketopyrimidines exhibit, in relation to the solution spectra in water, marked hypochromicity (33–69 per cent) and red shift of the long wavelength edge of the absorption (2000–3000 cm‐1) indicative of resonance intermolecular interaction and mixing of different electronic states. In most cases dimerization appeared the only photochemical reaction and the stereochemical form of main dimer corresponded with the predicted one on the basis of known crystal structure of the monomer. Initial quantum yields of monomer disappearance varied from solid to solid in the range of 0.1‐0.9 M/Einstein being, apparently, to a degree dependent on the separation between nearest‐neighbour C=C bonds. Reaction mechanism is discussed in terms of involvement of s

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06006.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—A proposed mechanism for the photochemical addition ofL‐cysteine to uracil with the concurrent formation of dihydrouracil is shown to proceed through the triplet excited state of uracil which can abstract hydrogen atoms from cysteine to form dihydrouracil. This triplet state is the same one as that leading to photodimerization. The thiyl radicals generated add to ground state uracil molecules. The data permit a re‐evaluation of the quantum yield for intersystem crossing of uracil in water which shows dimerization in aqueous solution to have a maximum efficiency of 56 per cent. The formation of the cross‐adduct and dihydrouracil may be sensitized but the efficiency of the reaction is related to the ability of the sensitizer to be photoreduced and not to its triplet

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06007.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—The kinetics of phytochrome transformation were examined over a 30°C temperature range (+5° to–25°C) in 75% glycerol. Two new intermediate reaction stages are described for the transformation of the red‐absorbing form,Prto the far‐red absorbing form,PfrThe free energies, enthalpies and entropies of activation were obtained for five of the six reaction stages observed in the transformation ofPrtoPfrand for the two reaction stages observed in the reverse process. All exhibited positive entropies of activation with the maximum being 25 entropy units. The results suggest that the phototransformations betweenPrandPfrconsist of relaxation processes beginning with the intermediate produced immediately upon absorption of a quantum of light and ending with eit

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06008.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06009.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY