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1.
When a reticulocyte lysate, supplemented with hemin, was warmed at 42 °C, its protein-synthesizing activity was greatly decreased. This was accompanied by the reduced formation of the 40 S·Met-tRNA f initiation complex. This complex preformed at 34 °C, however, was stable and combined with added globin mRNA and the 60 S ribosomal subunit to form the 80 S complex at the elevated temperature. When the ribosome-free supernatant fraction of lysates was warmed at 42 °C with hemin and then added to the fresh lysate system, it inhibited protein synthesis by decreasing the formation of the 40 S complex. This decrease in protein synthesis by warmed lysates or warmed supernatant could be overcome by high concentrations of GTP and cyclic AMP. This effect of GTP and cyclic AMP was antagonized by ATP. The results indicate that the inactivation of protein synthesis by the lysate warmed at 42 °C is due to the formation of an inhibitor in the supernatant. The ribosomal KCl extract prepared from the lysate that had been warmed at 34 °C and then incubated at this temperature for protein synthesis supported protein synthesis by the KCl-washed ribosome at both 34 and 42 °C. On the contrary, the extract from lysates that had been warmed at 42 °C and then incubated at 34 °C could not support protein synthesis at 42 °C, although it was almost equally as promotive as the control extract in supporting protein synthesis at 34 °C. The results indicate that the factor which can protect protein synthesis against inactivation at 42 °C is itself inactivated in lysates warmed at 42 °C. However, the activity of this extract to support formation of the ternary complex with Met-tRNA f and GTP was not reduced. Native 40 S ribosomal subunits isolated from lysates that had been warmed at 42 °C and then incubated for protein synthesis indicated that the quantity of subunits of density 1.40 g/cm 3 in a CsCl density gradient were decreased while those of density 1.49 g/cm 3 were increased. The factor-promoted binding of Met-tRNA f to the 40 S subunit of lower density from the warmed and unwarmed lysates was equal, suggesting that the ribosomal subunit was not inactivated. These results were discussed in terms of the action of the inhibitor formed in the supernatant at 42 °C, which may inactivate a ribosomal factor essential for protein synthesis initiation. 相似文献
2.
Phage CP-51 was rapidly inactivated when stored at the usual refrigerator temperatures (2 to 4 C) and even more rapidly when exposed to 0 C. The loss in viability resulting from exposure to cold appeared to correlate with the increase in number of phage particles having contracted tails. High concentrations (0.01 M) of Mg 2+, Ca 2+, or Mn 2+ stabilized the phage considerably, but even in the presence of these divalent cations, it was much less stable at 0 C than at 15 C. 相似文献
3.
Chlorosulphate NaMgSO 4Cl phosphor doped with Ce 3+ and co‐doped by Dy 3+ prepared by the wet chemical method was studied for its photoluminescence and thermoluminescence (TL) characteristics. The emission spectrum of Ce 3+ shows dominant peaks at 346 nm (excitation 270 nm) due to 5d → 4f transition. Efficient energy transfer occurs from Ce 3+ → Dy 3+ ions. Dy 3+ emission at 485 nm and 576 nm is due to 4 F 9/2 → 6H 15/2 and 4 F 9/2 → 6H 13/2 transitions of Dy 3+ ion respectively. The TL glow curves of NaMgSO 4Cl:Ce and Ce,Dy have been recorded for various concentrations at a heating rate of 2 °C/s irradiated by γ‐rays at a dose rate of 0.995 kGy/h for 1 Gy, which peaks at about 241 °C and 247‐312 °C respectively. Further, in changing the concentration level, the general structure of the intensity is found to increase. The main property of this phosphor is its sensitivity even for low concentrations of rare earth ions and low γ‐ray dose. There is still scope for higher doses of γ‐radiation. The phosphor presented may be used as a lamp phosphor as well as for TL studies. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
4.
Transduction of plasmid pBR322 by cytosine-substituted T4 phages has been studied. Three T4 phage mutants which substitute cytosine for all of hydroxymethylcytosine residues in the DNA, were shown to transduce pBR322 at frequencies of 2 × 10 ?2 to 4 × 10 ?3 transductants per singly infected cell. Also, three T4 phage strains which partially substitute cytosine for hydroxymethylcytosine, transduced pBR322 at frequencies of 2 × 10 ?3 to 2 × 10 ?4. The transduction frequencies of pBR322 we attained are at least 10-fold higher than those reported by G. G. Wilson, K. Young, and G. J. Edlin (1979, Nature (London)280, 80–82). We found that multiplicity of infection in preparation of the transducing phage is the most important factor affecting the frequency of pBR322 transduction. When a lysate made at a multiplicity of infection ranging from 0.5 to 0.05 was used as the donor phage, transduction frequency of pBR322 was 10- to 40-fold higher than that of high-m.o.i. lysate. The transduction frequency was not affected by either restriction systems or amber suppressors of the recipient cells. However, no pBR322-containing transductant was obtained when either recA or polA mutants were used as the recipients. DNA from T4dC phage containing pBR322-transducing particles was analyzed on agarose gel electrophoresis after cleavage with restriction endonucleases. It was suggested that the pBR322 DNA in the T4dC phage particles exists as head-to-tail concatemers. 相似文献
5.
Aims: Characterization of four virulent Lactococcus lactis phages (CHD, QF9, QF12 and QP4) isolated from whey samples obtained from Argentinean cheese plants. Methods and Results: Phages were characterized by means of electron microscopy, host range and DNA studies. The influence of Ca 2+, physiological cell state, pH and temperature on cell adsorption was also investigated. The double‐stranded DNA genomes of these lactococcal phages showed distinctive restriction patterns. Using a multiplex PCR, phage QP4 was classified as a member of the P335 polythetic species while the three others belong to the 936 group. Ca 2+ was not needed for phage adsorption but indispensable to complete cell lysis by phage QF9. The lactococci phages adsorbed normally between pH 5 and pH 8, and from 0°C to 40°C, with the exception of phage QF12 which had an adsorption rate significantly lower at pH 8 and 0°C. Conclusions: Lactococcal phages from Argentina belong to the same predominant groups of phages found in other countries and they have the same general characteristics. Significance and Impact of the Study: This work is the first study to characterize Argentinean L. lactis bacteriophages. 相似文献
6.
The effects of temperature, irradiance, and desiccation on the photosynthesis of a cultivated Japanese green alga Caulerpa lentillifera (Caulerpaceae) were determined by a pulse amplitude modulation (PAM)-chlorophyll fluorometer and dissolved oxygen sensors. The photochemical efficiency in the photosystem II (Fv/Fm and ΔF/Fm') during the 72-h temperature exposures (8, 12, 16, 20, 24, 28, 32, 36, and 40°C) was generally stable at 16–32°C but quickly dropped at lower and higher temperatures. The photosynthesis–temperature curve at 200 μmol photons m?2 s?1 also revealed that the maximum gross photosynthesis (GPmax) occurred at 30.7°C (30.5–30.9, 95% highest density credible intervals). Photosynthesis–irradiance curves at 16, 24, and 32°C quickly saturated, then expressed photoinhibition, and revealed that the maximum net photosynthetic rates (NPmax) and saturation irradiance (Ek) were highest at 32°C and lowest at 16°C. Continuous 6-h exposure to irradiances of 200 (low) and 400 (high) μmol photons m?2 s?1 at 16, 24, and 32°C expressed greater declines in their ΔF/Fm' at 16°C, revealing chronic chilling-light stress. The response to continuous desiccation (~480 min) under 50% humidity at 24°C showed that ΔF/Fm' dropped to zero at 480-min aerial exposure, and the treatments of more than 60-min desiccation did not return to the initial level even after 24-h subsequent rehydration in seawater. Likewise, ΔF/Fm' fell when the absolute water content (AWC) of the frond dropped below AWC of 90% and mostly did not return to the initial level even after 24-h subsequent rehydration in seawater, signifying a low tolerance to desiccation. 相似文献
7.
Photosynthetic CO 2 uptake and chlorophyll (Chl) a fluorescence of C 4 perennial grasses, Miscanthus floridulus (Labill) Warb and M. transmorrisonensis Hayata, from altitudes in central Taiwan of 390 and 2700 m, respectively, were studied at 10 and 25 °C to find if the species differ in their photosynthetic responses to a low temperature, and whether their photosystems 2 become more susceptible to the photoinhibition at low temperatures. For both species, the maximum photosynthetic rate (P max) was reduced when the leaves were exposed to 10 °C. At irradiances higher than 400 µmol m -2 s -1, the values of F v/F m were reduced in both species at 10 °C but not at 25 °C, which indicated the photoinhibition at 10 °C. Reductions in P max and the values of F v/F m at 10 °C were lesser in M. transmorrisonensis than in M. floridulus. 相似文献
8.
The oxidation enthalpy of reduced flavin mononucleotide at pH 7.0 in 0.2 m phosphate buffer has been studied by determining the heat associated with the reaction: FMNH 2 + 2 Fe(CN) ?36 ? FMN + 2 Fe(CN) ?46 + 2 H +. (a) (The quinone, semiquinone, and hydroquinone forms of FMN are represented as FMN, FMNH, and FMNH 2, respectively.) Calorimetric experiments were performed in a flow microcalorimeter which was modified to prevent sample contamination by oxygen. The enthalpy observed for reaction (a), after correction for dilution and buffer effects, was ?39.2 ± 0.4 kcal (mole FMNH 2) ?1 at 25 °C. The potential difference, ΔE′, developed by reaction (a) was determined potentiometrically and corresponded to a free energy change, ΔG′, of ?30.3 kcal (mole FMNH 2) ?1. The resulting entropy change, ΔS′, was thus calculated to be ?29.8 e.u. Reaction (a) was also studied at temperatures of 7 °C and 35.5 °C. ΔCp′ for the reaction was calculated as ?155 ± 18 cal deg ?1 (mole FMNH 2) ?1 at 20 °C. ΔH′ for the reaction (b), FMNH 2 ? FMN + H 2, (b) was calculated as +14.2 ± 0.7 kcal mole ?1 at 25 °C, relative to the enthalpy of the hydrogen electrode being identically equal to zero at all values of pH and temperature. The free energy at pH 7.0 for reaction (b), calculated from the potential was found to be ?9.7 kcal mole ?1, which resulted in an entropy for reaction (b) of 80.2 e.u. A thermal titration of reaction (a) was used to calculate the thermodynamic parameters for the formation of semiquinone dimer according to the reaction FMNH 2 + FMN ? (·FMNH) 2. (c) The free energy, enthalpy, and entropy changes for reaction (c) were estimated to be ?6.1 kcal mole ?1, ?7 kcal mole ?1, and ?3 e.u., respectively. 相似文献
9.
Europium trivalent (Eu 3+)‐doped Y 2O 3 nanopowders of different concentrations (0.5, 2.5, 5 or 7 at.%) were synthesized by the sol‐gel method, at different pH values (pH 2, 5 or 8) and annealing temperatures (600°C, 800°C or 1000°C). The nanopowders samples were characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), Fourier transform infrared spectroscopy (FT‐IR) and steady state photoluminescence spectroscopy. The effect of pH of solution and annealing temperatures on structural, morphological and photoluminescence properties of Eu 3+‐doped Y 2O 3 were studied and are discussed. It was found that the average crystallite size of the nanopowders increased with increasing pH and annealing temperature values. The Y 2O 3:Eu 3+ material presented different morphology and its evolution depended on the pH value and the annealing temperature. Activation energies at different pH values were determined and are discussed. Under ultraviolet (UV) light excitation, Y 2O 3:Eu 3+ showed narrow emission peaks corresponding to the 5D 0–7F J (J = 0, 1, 2 and 3) transitions of the Eu 3+ ion, with the most intense red emission at 611 assigned to forced electric dipole 5D 0→ 7F 2. The emission intensity became more intense with increasing annealing temperature and pH values, related to the improvement of crystalline quality. For the 1000°C annealing temperature, the emission intensity presented a maximum at pH 5 related to the uniform cubic‐shaped particles. It was found that for lower annealing temperatures (small crystallite size) the CTB (charge transfer band) position presented a red shift. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
10.
Photosynthetic CO 2 uptake and chlorophyll (Chl) a fluorescence of C 4 perennial grasses, Miscanthus floridulus (Labill) Warb and M. transmorrisonensis Hayata, from altitudes in central Taiwan
of 390 and 2700 m, respectively, were studied at 10 and 25 °C to find if the species differ in their photosynthetic responses
to a low temperature, and whether their photosystems 2 become more susceptible to the photoinhibition at low temperatures.
For both species, the maximum photosynthetic rate (P max) was reduced when the leaves were exposed to 10 °C. At irradiances higher than 400 μmol m -2 s -1, the values of F v/F m were reduced in both species at 10 °C but not at 25 °C, which indicated the photoinhibition at 10 °C. Reductions in P max and the values of F v/F m at 10 °C were lesser in M. transmorrisonensis than in M. floridulus.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
11.
Giant T4 bacteriophage were found by Doermann et al. (1973 a) with point mutants in gene 23 and by Cummings et al. (1973) after l-canavanine induction followed by an arginine chase. We now find T4 giant phage with 14 out of 15 tested temperature-sensitive mutants in gene 24 grown at intermediate temperatures between 33 °C and 37 °C.For one of these mutants, T4,24( tsB86), we found that (a) the optimum temperature for giant phage production is 34.8 °C, (b) the head-length distribution peaks sharply between 10 and 12 normal T4 phage head lengths, (c) about 75% of our giant phage have two tails, (d) the buoyant density in CsCl is greater than that of normal phage, (e) they are infectious and show an increased u.v. resistance, (f) their sodium dodecyl sulphate gel electrophoresis pattern is qualitatively similar to that of normal T4 phage, although the relative intensities of some of the bands are different, showing for example, a decreased 2 ratio, (g) optical diffraction and filtering of the flattened cylindrical part of the giant heads show a p6 surface net with a lattice constant of approximately 130 Å, a unique ratio of and a capsomer morphology of the type 1 + 6 + 6.Mixed infections with T4 wild type and T4.24( amN65) also yield giant phage. These are produced in highest amounts with a multiplicity of infection ratio of 5:5; no giants are observed at ratios of 1:9 or 9:1, suggesting that their formation may be caused by a dosage effect of P24. 相似文献
12.
In this study, a series of LaNbTiO 6:RE 3+ (RE = Tb, Dy, Ho) down‐converting phosphors were synthesized using a modified sol–gel combustion method, and their photoluminescence (PL) properties were investigated as a function of activator concentration and annealing temperature. The resultant particles were characterized using X‐ray diffraction, transmission electron microscopy, scanning electron microscopy, UV/Vis diffuse reflectance spectroscopy and PL spectra. The highly crystalline LaNbTiO 6:RE 3+ (RE = Tb, Dy, Ho) phosphors with an average size of 200–300 nm obtained at 1100°C have an orthorhombic aeschynite‐type structure and exhibit the highest luminescent intensity in our study range. The emission spectra of LaNbTiO 6:RE 3+ (RE = Tb, Dy, Ho) phosphors under excitations at UV/blue sources are mainly composed of characteristic peaks arising from the f–f transitions of RE 3+, including 489 nm ( 5D 4 → 7F 6) and 545 nm ( 5D 4 → 7F 5) for Tb 3+, 476 and 482 nm ( 4F 9/2 → 6H 15/2) and 571 nm ( 4F 9/2 → 6H 13/2) for Dy 3+, and 545 nm ( 5F 4 + 5S 2 → 5I 8) for Ho 3+, respectively. The luminescent mechanisms were further investigated. It can be expected that these phosphors are of intense interest and potential importance for many optical applications. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
13.
The growth of Nile tilapia Oreochromis niloticus (0·02–20·00 g) was measured when fed to excess during the hours of light, following their exposure to five thermal regimes fluctuating around the thermal optimum for growth ( Topt = 30° C) over the diel cycle of day (light, L) and night (dark, N), i.e. 27° C(L):33° C(N), 28·5° C(L):31·5° C(N), 30° C(L):30° C(N), 31·5° C(L):28·5° C(N) and 33° C(L):27° C(N) (two replicates per treatment, six weeks' rearing, growth measurements at weekly intervals). A model constructed with a stepwise multiple‐regression analysis accounted for 87·4% of the variation of the specific growth rate ( G, % M day ?1) from the variations of wet mass ( M), the extent of the thermal fluctuation ( FT) and their interactions, i.e. log 10G = 1·7686 ? 0·2136 log 10M + 0·0806 [log 10M× log 10 (1 + FT)] ? 0·0394 [log 10M× log 10 (1 + FT)] 2. Based on this model, the thermal fluctuation that produces the fastest growth ( ,°C) decreases in a curvilinear way, from 5·1° C at 20 mg to c. 0·7° C at 20 g. Thermal regimes that produce the slowest growth also produce the highest size heterogeneity. Functional hypotheses behind the size‐dependent effects of thermal fluctuations are discussed, together with their implications in natural habitats and aquaculture systems with in different contexts of food availability. 相似文献
14.
Thalli of Xanthoparmelia somloensis with natural content of polyols (control) and polyol-free thalli (acetone-rinsed) were used to study ribitol effects at low temperatures. Thalli segments were cultivated in ribitol concentration of 32 or 50 mM for 168 h at temperatures +5, 0, and ?5 °C. The chlorophyll fluorescence parameters (potential yield of photochemical reactions in PS 2 (variable to maximum fluorescence ratio, F v/F m), effective quantum yield of photochemical reactions in PS 2 (Φ PS2), and non-photochemical quenching (NPQ) were monitored in 24-h intervals using an imaging system. The effect of 32 mM ribitol on F v/F m and Φ PS2 was apparent only at ?5 °C, however, the effect was seen throughout the whole exposure. Surprisingly, 50 mM ribitol concentration treatment led to a decrease in F v/F m and Φ PS2 and to an increase in NPQ values at ?5 °C, while no change was observed at 0 °C and +5 °C. Acetone-rinsing caused decrease of F v/F m, Φ PS2 and NPQ. 相似文献
15.
Thiolutin resistant mutants of can not support the development of phage P22 at high temperature (40°C). Although normal amounts of phage DNA and lysozyme are synthesised, very few infectious particles are formed at higher temperature. The results indicate the involvement of host function in phage development. 相似文献
16.
A green chemical precipitation route was used to yield a hydrated basic sulfate precursor upon calcination at 1000°C into a series of (Y,Gd) 2O 2SO 4:Dy particles. The phosphors exhibited characteristic Dy 3+ emissions from 4F 9/2→ 6H J ( J = 15/2, 13/2, 11/2) transitions under ultraviolet light excitation; the quenching concentration of Dy 3+ was determined to be 2.5 at.%. Substitution of Gd 3+ for Y 3+ led to an additional strong sharp band at ~277 nm ( 8S 7/2→ 6I J transition of Gd 3+) in the photoluminescence excitation spectra, upon which the (Gd 0.975Dy 0.025) 2O 2SO 4 phosphor achieved a ~2.8-fold higher photoluminescence intensity via an effective energy transfer from Gd 3+ to Dy 3+ compared with the 354 nm excitation of Dy 3+. Both the photoluminescence and photoluminescence excitation intensities of (Y,Gd) 2O 2SO 4:Dy phosphors increased with rising Gd 3+ concentration and calcination temperature in the range 750–1000°C. A higher Gd 3+ concentration slightly prolonged the effective fluorescence lifetime. 相似文献
17.
Abstract Cytidine 3′,-5′-cyclic phosphate (cCMP) occurs in nature and has growth stimulatory activity on L-1210 cells. The initiation of cell growth by cCMP, under conditions where CAMP, cGMP and cUMP delay the onset of proliferation suggests that cCMP may play a regulatory role in the cell metabolism. It has been reported that in 3′,5′-cyclic nucleotides, the phosphate ring fused to the furanose ring resuicts the conformation of the furanose ring to the twist form C(3′) endo C(4′) exo ( 3T 4), in contrast to the C(2′) endo C(3′) endo ( 2T 3) and C(3′) endo C(2′) exo ( 3T 2) twist forms normally found in nucleotides and nucleosides. We have carried out an accurate crystal structure of cCMP and found that the furanose ring in cCMP has the C(3′) endo C(2′) exo conformation ( 3T 2), with a pseudo rotation amplitude (P) of 44° and phase angle τ m of 12°. cCMP is in low anti conformation (X CN = 15.4°) and O(5′) has the fixed g conformation. The phosphate ring is constrained to the chair conformation, as in other cyclic nucleotides. The two exocyclic P-O bond distances are short (1.489, 1.476Å) and the ring angle at N(3) is large (125.2°) suggesting that the molecule in the solid state is a zwitterion with a plus charge on N(3). The crystals are hydrated and highly unstable. The three water molecules are highly disordered in ten locations. The crystals of cCMP 3H 2O are hexagonal, a = 16.294(3), b = c = 11.099(4)Å, space group P6 1, final R value is 0.067 for 1620 reflections 230. 相似文献
18.
The F 1-ATPase isolated from pea cotyledon submitochondrial particles contained six types of subunit with molecular weights of 57 000 (α), 55 000 (β), 36 500 (γ), 26 500 (δ), 22 500 (δ′) and 8000 (ε). The same polypeptide composition was observed even when the purification was carried out at 4°C in the presence of proteolytic inhibitors, suggesting that the sixth subunit was not a proteolytic product formed during the isolation procedure. The six-subunit F 1-ATPase exhibited considerable cold stability: it retained 65% of its activity after 24 h of incubation at 0°C and was more than 90% active after 48 h of incubation at 4°C. The 26.5 kDa protein could be dissociated from the remaining F 1-ATPase by centrifugation in a linear sucrose gradient containing (NH 4) 2SO 4 and deoxycholate. The resulting five-subunit F 1-ATPase was considerably less stable at 0°C than the six-subunit enzyme. Several features suggest the possibility of a functional and structural relationship between the 26.5 kDa protein of the pea cotyledon mitochondria and the mammalian oligomycin-sensitivity-conferring protein. 相似文献
19.
A milk-clotting enzyme from Bacillus subtilis K-26 was purified by gel filtration and ion-exchange chromatography resulting in a 24-fold increase in specific activity with an 80% yield. Polyacrylamide gel electrophoresis and ultracentrifugel analysis revealed that the purified enzyme was homogeneous and had a molecular weight of 27,000 and a Km of 2.77mg/ml for κ-casein. The enzyme was most stable at pH 7.5 and showed increasing clotting activity with decrease in milk pH up to 5.0. The maximum milk-clotting activity was obtained at 60°C, but the enzyme was inactivated by heating for 30 min at 60°C. The enzyme was irreversibly inhibited by EDTA and unaffected by DFP. Heavy-metal ions (Hg 2+, Pb 2+) inactivated the enzyme. 相似文献
20.
Phospholipase activity has been found to be associated with T4 phage and T4 ghost particles. The attachment of the phospholipase to the phage persists during purification through cesium chloride gradients and dialysis, indicating that it is firmly bound. The presence of the enzymatic activity on T4 ghosts suggests that it is not normally packaged within the head of the virus. The enzyme has specificity for phosphatidylglycerol and its activity is stimulated by 0.1% Triton X-100 and 20% methanol. It does not have a requirement for Ca 2+ and is inactivated at temperatures above 60 C. The association of the phospholipase with T4 phage grown in a phospholipase-deficient host and its absence on unsuppressed T4 amtA3 suggests that it may be phage gene specific. 相似文献
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