摘要:

Abstract.–An analysis of the temperature dependence oftrans‐stilbene fluorescence yield in dipalmitoyl lecithin vesicles is used to obtain activation energies. The results are interpreted in terms of bilayer fluidity through and above the phase transition. Oxygen quenching of the fluorescence of pyrenebutyric acid (incorporated in dipalmitoyl lecithin and egg lecithin vesicles) is reported as a function of temperature and bulk oxygen concentration. Above the bilayer phase transition, quenching rates (determined by oxygen quenching) decrease with decreasing temperature. A reduction in oxygen quenching is observed through the dipalmitoyl lecithin phase transit

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07476.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.–A reaction scheme for the photolysis of 2‐oxo‐2,5‐dihydro‐1,3,4‐oxadiazoles is given by kinetic analysis, quantum yield measurement and product determination. The different reaction pathways in acetonitrile and ether ar

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07477.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.–The kinetics of photolytic tritium exchange at C(5) of [5‐T]cytidine are analyzed in terms of the rate of cytidine light absorption in order to demonstrate its light‐induced nature as opposed to spontaneous exchange from a stable photoproduct. Corrections must be included for an inner filter effect and a spontaneous C(5)‐tritium exchange both due to cytidine photohydrate produced during UV exposure. The quantum efficiency of this C(5)‐photoexchange process is of the same order of magnitude as that for cytidine photo

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07478.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.–Fluorescence detected magnetic resonance (FDMR) and fluorimetry have been used to study chlorophyll‐water complexes atT= 4.2 K. By combining these methods, zero‐field splitting (ZFS)‐parameters can be assigned to the triplet state of the various species. It is found that these parameters decrease upon aggregation and/or complexation. These results can be rationalized by using a simple free‐electron model for chlorophyll including excitonic interaction. Evidence is presented favouring a structure recently proposed by Shipman and Katz for a chlorophyll‐dimer involving hydrogen‐bonded water, present in non‐polar solutions at low temperature with spectral properties similar to those of chl

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07479.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.–An immunocytological method for detecting pyrimidine dimersin situhas been developed. The technique is based on the fixation in cell nuclei of radiolabelled antibodies directed against ultraviolet irradiated DNA. The relative amount of bound antibodies was estimated by radioautography. Pyrimidine dimers induced by a dose as low as 2 J m‐2can easily be detected. With this technique, the dose response of DNA photoproducts and their elimination by excision and photoreactivation were followed in eukaryotic cell cultu

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07480.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.–A large difference in survival occurs between buffered suspensions ofE. coliirradiated with UV radiation at a low fluence rate and those irradiated at a high fluence rate. For sufficiently large fluences, the extent of this fluence rate dependent recovery (FRR) is about two orders of magnitude greater than that which can be brought about by liquid holding recovery (LHR) following high fluence rate irradiation in most of theE. colistrains studied. LHR and FRR occur in excision resynthesis repair proficient (ERR+) but not ERR‐strains ofE. coli, although its observation can be masked in strains with complete repair potential upon subsequent growth on nutrient plates. Accumulation of DNA strand interruptions and excision of cyclobutyl dipyrimidine occur during LHR and FRR but are more extensive for the latter. Our data suggest mat events beyond incision and excision occur during LHR and FRR, but differences in the extent of ERR during LHR and FRR cannot account for the difference in cell survival between these two phenom

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07481.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.–Excision of cyclobutyl dipyrimidines from, and accumulation of strand interruptions in, DNA of different strains ofE. coliK12 were determined during liquid holding recovery after UV irradiation. The extent of PyrPyr excision was the same (20–25%) for both apolA mutant (E. coliP3478) and its parental wild type strain (E. coliW3110); however, single strand interruptions accumulate during liquid holding of polA cells, but not in the parental strain. In contrast, excision was greatly reduced in a mutant (KMBL 1789) which is defective in the 5′→3′ exonucleolytic function of DNA polymerase I. These data suggest that excision and resynthesis during liquid holding are carried out primarily, if not entirely, by DNA polymerase I. We further conclude that excision alone is both a necessary and sufficient condition to elicit liquid holding recovery, and that this excision requires a functional polymerase I 5′→ 3

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07482.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.–MDV‐1 RNA is a sequenced variant of Q/β RNA. This study analyzed the ultraviolet photosensitivity of the RNA with respect to its activity as template for the Q/β replicase reaction. An assay to measure the template activity is described and the quantum yield for inactivation of the template activity is shown to be 1.1 × 10‐3. Both uridine hydrates and pyrimidine dimers were found in the irradiated RNA. 1.4 hydrates were produced per lethal hit while less than 0.2 dimers were present per lethal hit. The production of uridine hydrates paralleled ultraviolet inactivation. It was concluded that hydrates were the significant lesion in irradiated M

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07483.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.–The absorption and fluorescence characteristics of subchloroplast particles highly enriched in P700 (1 P700 to 10–15 chlorophyllamolecules) and of two artificial systems are presented here. The fluorescence characteristics measured were excitation and emission spectra, and the degree of polarization of fluorescence. The model systems studied were chlorophyllaand pheophytin a in a polystyrene matrix, and a colloidal mixture of these two pigments with bovine serum albumin. Effects of 0.5% sodium dodecyl sulfate on the optical properties of the P700‐enriched particles are also described. The importance of pigment‐pigment and pigment‐protein interactions in determining the fluorescence properties of these particles are discussed. The possible role of pheophytin in these preparations needs further inve

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07484.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.–Although there have been several reports that divalent cations, especially Mg2+, can significantly affect chloroplast photoprocesses, the molecular mechanism of cation interaction is not well understood. We have investigated the interaction of Mg2+with Photosystem II photoprocesses by studying cation effects on chloroplast fluorescence and the Hill reaction. Our results are summarized as follows.1. Mg2+stimulation of background fluorescence (20–30%) saturates at about 0.5 mM Mg2+, while Mg2+stimulation of variable fluorescence (250%) saturates at about 2.5 mM Mg2+.2. Addition of Mg2+to chloroplasts treated with 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea or dithionite causes a doubling in the amount of total (background + variable) fluorescence.3. Studies on chloroplasts in the presence of 2,6‐dichlorophenolindophenol indicate that Mg2doubles the relative yield of variable fluorescence under light‐limiting conditions.4. Mg2causes large (70–120%) increases in the light‐limited rate of the DCIP Hill reaction.We interpret these results in terms of a model involving two components of chloroplast emission. Our analysis indicates that Mg2+increases the effective absorption cross section (size) of the pigment array associated with Photosyste

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07485.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY