摘要:

Abstract—Using flash photolytic techniques and direct chemical measurements of the conversion of the substrate (conversion of thymine dimers in DNA to monomeric thymine), we have determined photolyase concentrations in partially purified preparations of soluble proteins from yeast and have determined under continuous intense light the forward rate constantk1for binding of the enzyme and its substrate under a variety of conditions. The ionic requirements and the sharp peak of ionic strength dependence are independent of the species of uni‐univalent salts used in the assay. At infinite dilution, thek1for denatured DNA, and its ionic strength dependence, both appear identical to the values for native DNA. Both unirradiated denatured and unirradiated native DNA inhibit binding, denatured DNA being 10‐ to 20‐fold more effective. These combined factors have been taken into account to devise a sensitive assay for photoreactivable lesions in unlabeled DNA by competition in a flash photoreactivation reaction. The assay is used to measure dark repair inMicrococcus luteusin complete medium. After a dose of 100 J/m2the wild type of this organism removes photoreactivable lesions (pyrimidine dimers) from its DNA with a half‐time of 7 mi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06530.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Porous Vycor glass samples containing adsorbed molecules were illuminated at 77 K by a mercury lamp jacketed by a filter cutting off wavelengths below 250 nm. Oxygen or carbon dioxide on Vycor produces an asymmetric electron paramagnetic resonance (EPR) signal best described as holes trapped in the glass. Methyl bromide produces an identical EPR signal plus four other lines due to methyl radicals. Evidence is presented that the products result from excitonic energy transfer from the Vycor to the adsorbed materials. Triphenylamine (TPA) adsorbed on Vycor can also be photoionized by similar illumination, and the cation radical TPA+can be stabilized at 77 K if an electron acceptor is also adsorbed. Attachment of the photoejected electron by carbon dioxide forms CO2‐, and that by methyl bromide leads to methyl radicals. The CH3radical yield is dependent on the surface separation between the electron donor (TPA) and the acceptor (CH3Br). By monitoring the relative quantum yield of the methyl radicals as a function of distance separating the TPA and CH3Br, it is shown that the photoelectron is capable of migrating on the Vycor glass surf

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06531.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Fluorescence excitation spectra of all‐transretinal and the related polyene hydrocarbons anhydrovitamin A and diphenyloctatetraene show that only retinal has a wavelength‐dependent fluorescence quantum yield. Three possibilities for the unusual quantum yield behavior of retinal are considered. We conclude that competition between a fast radiationless process (perhaps of photochemical origin) and internal conversion between1ππ* states and a low‐lying1nπ* state provides the best rationalization for the data n

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06532.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Photodynamic properties of a tryptophan ultraviolet‐photooxidation product,N‐formylkynurenine, were investigated with amino acids and nucleotides as substrates. Steady‐state kinetic studies are presented as a function of sensitizer, substrate, oxygen concentration and pH. Involvement of singlet oxygen has been suggested for the sensitized oxidation of histidine and tryptophan. For the latter, 02‐is suggested as a supplementary oxidizing species. Lifetime computations from kinetic and quenching experiments suggest that sensitization occurs via theN‐formyl‐kynurenine triplet state. The importance of the photodynamic properties ofN‐formyl‐kynurenine in protein and DNA photochemistry is discussed.RésuméLes propriétés photodynamiques d'un produit de photooxydation ultraviolette du tryptophane, laN‐formyl‐cynurénine, ont étéétudiées vis‐à‐vis d'acides aminés et de nucléotides tenant lieu de substrats. La cinétique de l'action photodynamique a étéétudiée en fonction des concentrations en sensibilisateur, en substrat et en oxygène, et en fonction du pH. La participation de l'oxygène singulet a été mise en évidence dans l'oxydation sensibilisée de l'histidine et du tryptophane. Pour ce dernier, nous suggérons l'intervention de O2‐comme agent oxydant supplémentaire. A partir d'expériences cinétiques et d'extinction, le calcul du temps de vie de l'état excite du sensibilisateur initiant la réaction suggère que ce dernier est l'état triplet. L'importance des proprifétés photodynamiques de laN‐formyl‐cynur

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06533.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Rare‐earth metal ions give 1:1 complexes with hen's egg‐white lysozyme. Spectroscopic and enzymic activity measurements suggest that the binding site consists of the side chains of glutamic‐35 and aspartic‐52. The spatial conformation of these complexes is practically identical to that of native lysozyme, especially as concerns the environment of the tryptophyl side chains. Irradiation of La3+‐lysozyme by visible light, in the presence of proflavine as photosensitizer, causes the oxidative modification of all the tryptophyl and methionyl residues at almost the same rate as in uncomplexed protein. On the other hand, when lanthanide ions with nonvanishing magnetic moments were coordinated with lysozyme, at least some tryptophans and methionines were protected from photooxidative attack. The distance of the protected residues from the coordination site increased with increasing magnetic moment of the bound metal ion, which suggests that inhibition of the photoprocess was mainly due to perturbation of the lifetime of the electronically excited intermediate species. On the basis of the atomic coordinates of lysozyme in the crystal state, it is thus possible to define a “quenching radius” for the various lanthanide ions; these radii could in turn be used to evaluate intramolecular distances in proteins of unknown tertiary structure, by identifying the amino acid residues that are protected or photooxidized upon irradiation of complexes between the given protein and several different lanthanide ions. Our studieson lysozyme allow us to define five radii of protection, ranging from 6·7 Å for Sm3+to over 17 Å for Dy3+, Ho3+, Er3+and Tb3+. Therefore, this technique opens the possibility of mapping appreciably large regions of

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06534.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—The absorption spectrum of lycopene can be altered to show significant absorption in the 350–360 nm region in an ethanol‐water mixture, thus resembling the phototropic action spectrum ofAvenacoleoptiles. The hypochromicity (bleaching) of the main absorption band and appearance of the new band at 350–360 nm can be attributed to exciton interactions between two stacked lycopene molecules. β‐Carotene does not show anomalous bleaching under identical conditions. Thus, the apparent modification of the absorption spectra of carotenoids in ethanol‐water mixtures cannot be used as an argument to resolve the action spectrum in terms of carotenoids. In addition, we have critically reviewed the spectroscopic characteristics of carotenoids. Short lifetimes of the excited singlet states and inefficient intersystem crossing of carotenoids are not compatible with the suggestion that carotenoids are the most likely candidate for the photoreceptor pigment in

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06535.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Kinetics of the bacteriochlorophyll (P870+) electron paramagnetic resonance signal photo‐induced at room temperature in whole‐cellRhodospirillum rubrumexhibit transients which are strongly dependent upon the light‐dark history of the cells. This paper reports a study of these kinetics as a function of actinic light intensity, light‐dark history, temperature and applied microwave power. The simplest interpretation of the observed complexities in the kinetic curves is that the rate of formation and the rate of decay of P870+are controlled by slow dark reactions of the electron‐transport chain, and that the rate‐controlling reaction is variable during the transition from a dark‐adapted to a steady state in the light. With this interpretation, it is possible to measure or to infer order‐of‐magnitude estimates of the lifetimes of some of

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06536.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06537.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06538.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06539.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY