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Optical rotatory dispersion studies have been carried out at temperatures up to 150 °C. on poly(γ-benzyl L -glutamate) in α-chloronaphthalene and N-methylcaprolactam, and on poly-ε-carbobenzoxy-L -lysine, poly-δ-carbobenzoxy-L -ornithine, and poly(L -glutamic acid) in N-methylacetamide. The Moffitt-Yang ?b0 values were large in all cases, but significant decreases in ?b0 were observed at the upper temperature limits of the study suggesting that a transition region was being entered. Polymer degradation generally precluded examination of the systems through the suggested transition region. 相似文献
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Correlation between surfactant/micelle structure and the stability of bacteriorhodopsin in solution.
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The rate of solubilization and isothermal bleaching of bacteriorhodopsin (bR) in a series of nine alkylammonium surfactants is studied by using time-resolved optical spectroscopy. The surfactant series RN(+)R'(3) covers a range in tail length (R = C(12)H(25), C(14)H(29), or C(16)H(33)) and headgroup size and hydrophobicity (R' = CH(3); C(2)H(5), or C(3)H(7)). The rate of bleaching increases initially with increasing surfactant concentration but decreases at higher concentrations. Possible explanations for this behavior are discussed. The kinetic data are consistent with the penetration of the surfactant into the protein interior. Interaction of the surfactants with the protein is a complicated, multistep process, and the rate curves are a function of at least four variables: 1) the micellar environment, 2) the length of the surfactant tail, 3) the size of the headgroup, and 4) the hydrophobicity of the headgroup. Our data provide new insights into the molecular characteristics that help define the performance of surfactants in the solubilization and denaturation of membrane-bound proteins. 相似文献
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Velikodvorskaya GA Tikhonova TV Gurvits ID Karyagina AS Lavrova NV Sergienko OV Tashlitskii VN Lunina NA Lunin VG 《Applied and environmental microbiology》2010,76(24):8071-8075
Recombinant plasmids containing fusion proteins composed of two different modules were constructed and expressed in Escherichia coli. The modules encoded the lactase LacA (LacZ) from the thermophilic bacterium Thermoanaerobacter ethanolicus and the cellulase CelD, a cellulose-binding module (CBM) from Anaerocellum thermophilum. The CelD CBM provides a spontaneous and strong sorption of the fusion proteins onto a cellulose carrier. The enzymatic activities of both the free LacA protein and LacA-CelD CBM fusion proteins immobilized onto the cellulose carrier were assessed. The LacA activity of the fusion protein was dependent upon its position with respect to the CBM. The highest level of lactase activity and stability was observed when the lactase domain was localized at its N terminus. A continuous-flow column reactor of lactase immobilized on a cellulose carrier was constructed, and its activity was assessed. The lactose hydrolysis rate for a 150 mM (5%) solution at a flow rate of 1 reactor volume per min was 75%, which is a value optimal for further whey transformation into glucose/galactose syrup. 相似文献
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Chlorophyll a (Chl a) fluorescence-temperature profile in the region of 20–80°C was recorded for fourteen different plant species. In all the species studied, there was a rise in the fluorescence intensity in the region of 45–50°C and around 55°C the fluorescence intensity started to decline. In four of the species (Acacia melanoxylon, Ervatamia montana, Eucalyptus tertecornius and Azardicta indica) tested, there was a secondary rise in the fluorescence intensity around 65–70°C whereas in all other species a sharp decline in the fluorescence intensity was observed at this point. These changes in the fluorescence intensity at high temperatures (65–70°C) appear to be species specific and cannot be explained either in terms of changes in the stoichiometry between the two photosystems or in terms of Chl a fluorescence emission from photosystem I (PS I) at higher temperatures. This conclusion is supported by following observations: (1) there was no definite correlation between the Chl a/Chl b ratio and the pattern of fluorescence-temperature profile at high temperatures; (2) the sun and shade plants of the same species had a similar pattern of fluorescence-temperature profile; and (3) preferential excitation of PS I did not alter the fluorescence-temperature profile.Abbreviations Chl
chlorophyll
- PS
photosystem 相似文献
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Skin temperatures were measured on three Quechua Indian infants resident at 4,000 meters above sea level in Peru. Nape temperatures were warmer than other skin sites, suggesting that the brown adipose tissue associated with non-shivering thermogenesis is metabolically active despite the reduced oxygen availability at high altitude. The question of the role of non-shivering thermogenesis in infant thermoregulation under the covariant stresses of hypoxia and cold is still open. 相似文献
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Francesca Cardillo Theobaldo Elisabeth Lira Elisabeth Cheng Ayako Irokawa Mineko Tominaga 《Biotechnology Techniques》1991,5(1):73-76
Summary N-acetyl-tyrosine (Ac-Tyr-OH), N-t-butyloxycarbonyl-tyrosine (Boc-Tyr-OH) and N-benzyloxycarbonyl-tyrosine (Z-Tyr-OH) were esterified by alpha-chymotrypsin suspended in ethanol-buffer, 20.0:0.5 (v/v). The rates of esterification decreased in the order Ac-Tyr-OH > Z-Tyr-OH > Boc-Tyr-OH. For Z-Tyr-OH esterification the pH optimum depends on the nature of the buffer salt, being 4.0 for acetate and 6.0 for phosphate buffers. 相似文献
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David JR 《Journal de la Société de Biologie》2008,202(2):113-117
It is well known that in Mammals, spermatogenesis requires a temperature lower than that of the body. In Ectotherms, for example in Insects, male sterility/ fertility according to environmental conditions also remains a neglected field. In Drosophila melanogaster, a complete male sterility after development at 30 degrees C was described in 1971. A similar phenomenon, observed at low temperature, was described two years later. Recent comparative investigations have shown that what was found in D. melanogaster was also valid in other species. In each case, it is possible to define a range of temperatures compatible with a complete development. According to the investigated species, however, this range is very variable, for example 6-26 degrees C or 16-32 degrees C. In each case, the occurrence of sterile males is observed before the lethality threshold is reached. Such a phenomenon is probably important for understanding the geographic distributions of species. The cosmopolitan D. melanogaster lives under very different climates and exhibits corresponding adaptations. In countries with a very hot summer, such as India or the African Sahel, male sterility appears only at 31 degrees C. Crosses between a temperate population from France and a heat-resistant Indian population revealed that a large part of the genetic difference was carried by the Y chromosome. Such a result is surprising since the Y chromosome harbors only a very small number of genes. In conclusion, drosophilid species, during their evolution, were able to adapt to very different climates and the thermal sterility thresholds have changed, following these adaptations. But we still lack an evolutionary hypothesis for explaining why sterile males are, in all cases, produced at extreme, low or high temperatures. 相似文献
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The equation of state for a hydrogen plasma at high temperatures is considered in a physical and a chemical model. A simple expression is obtained that relates the pressure correction in chemical models to the high-temperature limit of the atom partition function. This expression ensures a correct asymptotic behavior of the equation of state in the high-temperature limit. It is explained why the familiar astrophysical model of Hummer, Mihalas, and Däppen, as applied to helioseismology, yields worse results than a physical model. A modification of the astrophysical model is proposed that makes it possible to use the nearest neighbor approximation to calculate the atom partition function in chemical models in solving astrophysical problems and problems concerning low-temperature plasmas. 相似文献
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Protein aggregation, being an outcome of improper protein folding, is largely dependent on the folding kinetics of a protein. Previous studies have reported a positive correlation between the stability of the secondary structural elements of a protein and their rate of folding/unfolding. In this in silico study, the secondary and tertiary structures of proteins a) that form inclusion bodies on overexpression in Escherichia coli, b) that form amyloid fibrils and c) that are soluble on overexpression in E. coli are analyzed for certain features that are known to be associated with structural stability. The study revealed that the soluble proteins seem to have a higher rate of folding (based on contact order) and a lower percentage of exposed hydrophobic residues as compared to the inclusion body forming or amyloidogenic proteins. The soluble proteins also seem to have a more favored helix and strand composition (based on the known secondary structural propensities of amino acids). The secondary structure analyses also reveal that the evolutionary pressure is directed against protein aggregation. This understanding of the positive correlation between structural stability and solubility, along with the other parameters known to influence aggregation, could be exploited in the design of mutations aimed at reducing the aggregation propensity of the proteins. 相似文献
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Helmut Cölfen Stephen E. Harding Emma K. Wilson Len C. Packman Nigel S. Scrutton 《European biophysics journal : EBJ》1996,24(3):159-164
Earlier studies using x-ray crystallography have shown that trimethylamine dehydrogenase (TMADH) from methylotropic bacteria exists as homodimers in the crystalline state. In this present hydrodynamic study we show that this is true also in dilute solution conditions and investigate the degree of swelling or relaxation of the protein in solution. Analytical ultracentrifugation was used to determine the molar mass and to investigate whether the homodimeric nature of this molecule in crystal form — as visualized by x-ray crystallography — is reproduced in dilute solution at temperatures between 4 and 40°C. The globular solution structure determined at 4 and 40°C is in good agreement with crystallographic data although trimethylamine dehydrogenase was found to be either more asymmetric in solution — or highly hydrated —, a phenomenon found to increase with temperature. In agreement with the crystallographic structure, the enzyme sediments as a homodimer with a molar mass of (163,000±5,000) g/mol. The concentration dependence of the sedimentation coefficient in the range of 0–1 mg/ml, indicates that no association or dissociation occurs. These findings are additionally supported by sedimentation equilibrium data in the concentration range of 0 to 1.8 mg/ml. Finally, from the sedimentation coefficient distribution at various temperatures, it was concluded that the enzyme is conformationally flexible and assumes an even more expanded structure at higher temperatures which is in good agreement with the hydrodynamic calculations performed.
Correspondence to: S. E. Harding 相似文献
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Ferdjani S Ionita M Roy B Dion M Djeghaba Z Rabiller C Tellier C 《Biotechnology letters》2011,33(6):1215-1219
The activity and stability of a β-glycosidase (Thermus thermophilus) and two α-galactosidases (Thermotoga maritima and Bacillus stearothermophilus) were studied in different hydrophilic ionic liquid (IL)/water ratios. For the ILs used, the glycosidases showed the best
stability and activity in 1,3-dimethylimidazolium methyl sulfate [MMIM][MeSO4] and 1,2,3-trimethylimidazolium methyl sulfate [TMIM][MeSO4]. A close correlation was observed between the thermostability of the enzymes and their stability in IL media. At high IL
concentration (80%), a time-dependent irreversible denaturing effect was observed on glycosidases while, at lower concentration
(<30%), a reversible inactivation affecting mainly the k
cat was obtained. The results demonstrate that highly thermostable glycosidases are more suitable for biocatalytic reactions
in water-miscible ILs. 相似文献