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51.
52.
Jan J. B. Boesen Sandrine Stuivenberg Corné H. M. Thyssens Henk Panneman Firouz Darroudi Paul H. M. Lohman Jo W. I. M. Simons 《Molecular & general genetics : MGG》1992,234(2):217-227
Summary Cells of the mouse T-lymphoma line GRSL13 were treated with 8-methoxy-psoralen plus longwave ultraviolet light (PUVA) under conditions where the biological effects are mainly due to non-persistent DNA crosslinks (PUVA-CL treatment). Fluctuation analysis showed that PUVA-CL treatment resulted in an enhancement of the mutation rate in the progeny of treated cells, which persisted until the eleventh generation after treatment. Since only 5 cross-links are available to account for 52 mutational events observed in the coding region, about 90% of the induced mutational events must have been untargeted. This was confirmed by molecular analysis of these mutations, which showed that 53% of the point mutations arose at sites which are not a target for psoralens. This supports the hypothesis that stress responses may give rise to untargeted mutagenesis. Further support for this hypothesis is provided by the observation that 8-methoxy-psoralen (8-MOP) or UVA alone (both of which are known to induce many pleiotropic effects) each acted as indirect mutagen by enhancing the mutation rate 2–4 fold in the progeny of treated cells. 相似文献
53.
Racemization of the aqua-{N-salicylidene-(S)-alaninato}copper(II) by reaction with potassium cyanate
Copper(II) N-salicylidene-(S)-alaninate trihydrate reacting as the S-enantiomeric parent compound with KOCN in hot diluted methanol yielded by slow crystallisation from the cooled reaction mixture (in the course of 1 day) the racemic product K[Cu{sal-(RS)-ala}(NCO)]. The parameters of the axial type EPR spectrum in X-band region and the LF band position in the electronic spectrum are typical of an axially distorted square pyramidal coordination of the Cu(II) atom in this complex. The spectral properties of the complex cuprate prepared and its basal crystallographic data are consistent with those of the earlier studied15 K2[Cu2{sal-(RS)-ala}2(μ-NCO)2] synthetized by using [Cu{sal-(RS)-ala}(H2O)].H2O as the racemic parent complex in the reaction mixture with KOCN. 相似文献
54.
The thermophilic blue-green alga Synechococcus lividus was grown at 38 and 55°C. The reaction center chlorophyll-protein complexes (CP) of Photosystem (PS I) and PS II, CP aI and CP aII, were isolated by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis at 4°C. SDS solubilization of thylakoids was performed in the temperature range 0–65°C. The low-temperature absorption and fluorescence emission spectral properties of the isolated chlorophyll-protein complexes were analyzed. Only traces of CP aI were solubilized at temperatures below the lipid phase transition temperature. Instead, a minor PS I component, CP a′I, was obtained that had absorption and fluorescence characteristics similar to those of CP aI. CP a′I had a slightly lower mobility than CP aI in SDS-polyacrylamide gel electrophoresis. The amount of CP aI in the gel scan profile increased dramatically when solubilization was carried out above the phase transition temperatures, but started to decrease above 60°C. CP aII, on the other hand, could be efficiently extracted even at 0°C and was stable in the scan profile up to extraction temperatures of 30–40°C. Low-temperature absorption and fluorescence emission spectra were typical for CP aI and CP aII and no specific effects of the two growth temperatures on these properties were observed. The phase transition temperature was considered to be critical for the solubilization of CP aI, either because of the difficulties of SDS (especially as it forms micelles at low temperatures) in penetrating the solidified membrane lipids at temperatures below that of the phase transition or because the CP aI monomers of the PS I antennae are so strongly bound to each other that they cannot be dissociated by SDS before thermal agitation has reached a certain level that is achieved above the phase transition temperature. We consider both the difficulties in solubilizing CP aI at sub-transition temperatures and the heat stability of the two complexes as adaptations which enable Synechococcus to grow under extreme high-temperature regimes. 相似文献
55.
(1) Three analogs of merocyanine dyes added to suspensions of chromatophore vesicles showed absorbance changes responding to the change in surface potential induced by salt addition and to the change in membrane potential induced by illumination. (2) The extent of the light-induced absorbance changes of the dyes was linearly related, in the presence and absence of uncouplers, to that of carotenoid spectral shift which is an intrinsic probe of the intramembrane electric field. (3) Comparison of the merocyanine absorbance changes induced by salt addition with those induced by illumination indicated that the surface potential change in the outer surface of chromatophore membranes during illumination was very small. (4) Judging from the spectra of these absorbance and from the low permeabilities of the dyes to membrane, the absorbance change are attributed to change in distribution of the dyes between the medium and the outer surface region in chromatophore membranes. The extent of the light-induced absorbance changes of merocyanine dyes depended on the salt concentration of the medium. The types of dependence were different among three merocyanine analogs. This is explained by the mechanism mentioned above assuming appropriate parameters. It is suggested that, under continuous illumination, an equilibrium of the electrochemical potential of H+ is reached between the bulk aqueous phase and the outer surface region in the membrane where the merocyanine dyes are distributed. 相似文献
56.
Under far-red (>650 nm) illumination Anacystis nidulans grows poorly and develops a low chlorophyll content. During continued culture over many generations there are increases in growth rate and in the chlorophyll/phycocyanin ratio, usually occurring in concomitant and stepwise fashion. From such selection cultures six clones have been established which differ from the parent in pigment content and show improved growth rate in far-red light. From the evidence at hand the six clones are presumed to be spontaneous mutants selected under the photosynthetically restrictive condition of far-red illumination. 相似文献
57.
Horst W. Luftensteiner 《Plant Ecology》1980,41(2):61-67
Summary A new system of dispersal units has been elaborated, based on weight and morphological features functional in dispersal. Weight was divided into eight classes and the functional morphological features were selected in such a way that their effectiveness could be tested by experiments.The spectra of weight and dispersal adaptations of dispersal units sampled in Euphorbio-Pinetum nigrae and Fumano-Stipetum habitats south of Vienna are calculated with this system and then compared.The results show that both communities can be characterized with such spectra. It is also possible with these spectra to make statements about the ecological and social position of the association in a succession.Nomenclature follows Ehrendorfer (1973). 相似文献
58.
Beate Ackermann-Schmidt Roland Süssmuth Franz Lingens 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1982,699(2)
The mutagen 1,1′-hexamethylene-bis[(5-p-chlorophenyl)-biguanide] reacts at 37°C with guanosine and guanine to yield xanthosine or xanthine and oxidizes cysteine to cystine. After treatment of a guanosine-labelled DNA sample from Escherichia coli with the mutagen xanthine could be detected as a reaction product. At a slow rate the mutagen is hydrolysed spontaneously yielding urea, 1,6-hexanediol and 4-chloroaniline. The reaction mechanisms both of the hydrolysis and of the reaction with cysteine and guanosine are discussed. 相似文献
59.
Rhodospirillum rubrum strain F24.1 is a spontaneous revertant of nonphototrophic mutant F24 derived from wild-type strain S1. Strain F24 shows no detectable photochemical activity and contains, at most, traces of the photoreaction center polypeptides. Strain F24.1 has a phototrophic growth rate close to that of the wild-type strain (Picorel, R., del Valle-Tascón, S. and Ramírez, J.M. (1977) Arch. Biophys. Biochem. 181, 665–670) but shows little photochemical activity. Light-induced absorbance changes in the near-infrared, photoinduced EPR signals and ferricyanide-elicited absorbance changes indicate that strain F24.1 has a photoreaction center content of 7–8% as compared to strain S1. Polyacrylamide gel electrophoresis of isolated F24.1 chromatophores shows the photoreaction center polypeptides to be present in amounts compatible with this value. Photoreaction center was prepared from strain F24.1 and showed no detectable difference with that of strain S1. It is concluded that strain F24.1 photosynthesis is due entirely to its residual 7–8% of typical photoreaction center. 相似文献
60.