摘要:

AbstractThe Förster theory of radiationless electronic excitation energy transfer was used to determine the intramolecular separation between the tyrosine and phenylalanine residues in leucine‐ and methionine‐enkephalin. The spectral overlap integrals and the Förster critical distances were evaluated. Transfer efficiencies were determined by observing sensitized fluorescence of the acceptor and quenching of the donor fluorescence. The results were compared with theoretical estimations, better agreement being obtained with the first m

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04408.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractTime‐resolved, low‐temperature resonance Raman spectra of triplet states of the carotenoids specifically present in bacterial reaction centers in a strainedcisconformation have been obtained, thus demonstrating the possibility of studying intermediate transient states of these structures using resonance Raman spectroscopy. Resonance Raman spectra of tripletcisspheroidene andcismethoxyneurosporene present in reaction centers ofRhodopseudomonas spheroides,(strains 2.4.1. and Ga, respectively) exhibit marked differences with those of triplet, all‐transcarotenoids previously studiedin vitro.These differences, together with the frequency shifts measured for thev1modes, indicate that triplet carotenoids bound to reaction centers retain acisconformation, and that probably no isomerization occurs to all‐transcarotenoids upon T ← S0excitation. Pielectron distributions along the polyene backbone are probably less regular in the triplet state than in the singlet ground state, although probably not to the extent suggested by previous theoretical calculations. The apparently anomalous behaviour of thev2bands of all‐transcarotenoids upon T ← S0excitation is shown to result largely from the actual complexity of this region of the Raman spectra, together with a weak participation of thevc—–cinternal coordinate in the corresponding modes. Finally, the Raman scattering efficiency of triplet spheroidene bound to reaction centers is lower than that of the singlet, ground state form, under equivalent exci

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04409.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThe photodynamic effects of α‐terthienyl (αT) in near‐UV light (UV‐A) onEscherichia colishowed close agreement with the light absorption of αT at different wavelengths suggesting that αT is the primary absorbing molecule responsible for the photosensitized reaction. Studies with DNA repair deficient mutants ofE. coliindicated that the bactericidal action of αT/UV‐A was not mediated by DNA damage, in direct contrast to the well‐known photosensitizer, 8‐methoxypsoralen. By using a closed borosilicate glass reaction vessel and various gas mixtures, it was demonstrated that photosensitization of bothE. coliand a more resistant bacterium,Pseudomonas aeruginosa, was absolutely dependent on the presence of oxygen. The rate of killing by αT/UV‐A showed a rather small dependence on preincubation temperatures, with quite rapid killing at 5°C, suggesting that the movement of αT across the cytoplasmic membrane ofE. coliis not the rate limiting step in killing and perhaps is not even necessary for killing. Sodium dodecyl sulphate‐polyacrylamide gels of cell membrane proteins after 15 and 30min of treatment with αT/UV‐A showed substantial random crosslinking of these proteins. The results taken overall suggest that αT is a photodynamic photosensitizer which exerts its primary effect at the level

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04410.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThe radiation response of stationary‐phase cells ofEscherichia colistrainsRT4(nur+) and RT2 (nur) was measured at 6 selected wavelengths between 254 and 405 ran. The relative response of thenur+. andnurstrains was almost the same at 254 and 290 nm. However, the differential sensitivity of the RT4 and RT2 strains (ratio of the initialF37values of thenur+to thenurstrains) was 2.7 at 313 nm, 3.2 at 334 nm, 3.1 at 365 nm, and 2.3 at 405 nm. Thus, the fluence enhancing effect of thenurgenotype extends over the wavelength range of approximately 300 to 420 nm. The substantial effect ofnurat 313 nm strongly suggests that the increased sensitivity of thenurstrain is the consequence of a repair deficiency that reduces the efficiency of mending DNA lesions produced by UVA (320–400 nm) and UVB (290–320 nm), but not UVC (200–290 nm) ra

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04411.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThe minimal erythema dose (MED) is often used as a quantity by which the influence of certain treatments of the skin can be measured. Differential measurements are performed by assessing the difference of the MED on the skin treated in some way and the untreated skin.As the MED‐measuring scale is discrete, the question is sometimes raised whether it is possible to measure differences smaller than one scale unit. In the present paper it is shown that this is indeed possible; in principle the discreteness of the scale does not impose any restriction on the smallest value of the difference that can be measured. The discreteness of the scale introduces an extra random variation into the measurement. This variation is estimated theoretically. It is automatically included in the usual error analysis.The discreteness variance is small when compared to other variance components, which are computed from an analysis of variance of actual experiments. Reducing the discreteness variance, by reducing the dose decrement of the MED‐measuring scale, therefore, does not enhance the overall accuracy considerably. Finally, it is found that the assessments of the MED by the various observers do not differ significantly from each other, and that multiple assessments do increase the accuracy, especially for small effe

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04412.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractA K+‐stimulated ATPase from suspension‐cultured rose cells was isolated and subjected to UV radiation. The characteristics of the ATPase resembled those of a plasma‐membrane associated enzyme and not those of the mitochondrial enzyme. The ATPase required Mg2+and was further stimulated up to 100% by K+. K+stimulation was specific for ATP. The order of stimulation by monovalent cations was K+>Na+>Li+. The enzyme had a pH optimum of 6.5 in the presence of 50 mM K+. It was almost completely inhibited by diethylstilbestrol and partially inhibited by vanadate. but was not affected by azide or oligomycin. The inhibition of ATPase activity by various fluences of UV indicated that one fraction of the K+‐stimulated activity was very sensitive to radiation, while another fraction was relatively insensitive. It is possible that UV distinguished between two enzymes. The action spectra for inhibition of both fractions showed maxima at 290 nm and significant but much lower action throughout the near‐UV region, resembling spectra in the literature for the inhibition of transport processes in

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04413.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractFluorescence lifetimes are reported for N‐all‐trans‐retinylidene‐n‐butylamine in hexane. Picosecond resolution was obtained by excitation with a single 355‐nm pulse, 25 ps FWHM, from a passive mode‐locked YAG‐laser and detection with a high speed streak camera. The lifetime dependence on temperature and the spectral characteristics support a vibrational‐torsional deactivation model of the singlet excited state of two different conformers. Additional data in decalin are consistent with this model, while the quenching in alcoholic solutions may be supported by the solv

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04414.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractCells of the photosynthetic purple bacteriumChromatium vinosumgenerate a transmembrane electrochemical proton gradient (δμH+H+) on illumination. The steady state values of the two components of δμH+m+, δpH and the membrane potential (δψ) have been measured as a function of both the pH and ion composition of the external medium. While δψ and δpH vary considerably as the external pH is varied from 5.5 to 7.5, the magnitude of δμH+h+remains relatively constant over this pH range. δψ is relatively unaffected by the ion composition of the medium but δpH and δμH+H+both vary considerably depending upon the cation present in the medium. The use of specific ionophores to eliminate either δpH or δψ results in changes in the magnitude of the other component. The δpH values determined here were used to predict the direction of Tl+flux via the potassium‐proton antiport and to demonstrate the reversib

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04415.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractFluorescence lifetimes (τf) of chlorophylla(Chia) have been measured by the single‐photon‐counting technique over a wide range of concentrations (˜10‐7˜10‐4M) in deoxygenated pyridine, diethyl ether, toluene and methanol. At pigment concentrations ˜1 μM, reabsorption of fluorescence induces significant artifacts on measured values of τfwhich are dependent on detection wavelength and the specific geometry of the experiment. There is a clear dependence of τfon the nature and degree of solvation, including both coordination of the central magnesium and hydrogen‐bonding of the solvent (viz. alcohols) to the macrocycle. Quenching of the excited singlet state by molecular oxygen was measured quantitatively in ether, and a bimolecular rate constant markedly slower than the diffusion‐controlled

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04416.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractFluorescence lifetimes (τf) of bacteriochlorophylla(BChla) have been measured by the method of time‐correlated single‐photon counting on dilute (1 μM) solutions of the pigment in 15 solvents. There is a pronounced dependence of τfon the nature of the solvent. Specifically, τf, is longer when the central magnesium is hexacoordinated than when pentacoordinated and shorter when the macrocycle is hydrogen‐bonded than when it is not, but the latter effect is more pronounced. Both trends were confirmed by parallel studies on bacteriopheophytina(BPheoa). Because of the short lifetimes (˜ 2.2–3.6 ns), quenching of fluorescence by molecular oxygen is not a significant factor in aerated solutions of the bacterial pigments. However, reabsorption artifacts are non‐negligible, which necessitates studies on dilute solutions. Fluorescence quantum yields (øf) have been estimated for BChlain 13 solvents by comparing the observed fluorescence lifetimes with the radiative lifetimes calculated from the integrated abs

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04417.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY