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1.
C.William Anderson H.Brian Halsall William R. Heineman George P. Kreishman 《Biochemical and biophysical research communications》1977,76(2):339-344
The E0′ values for the conversion of horse heart cytochrome from the oxidized to the reduced form as a function of temperature have been measured in 0.10 M NaCl, 0.10 M sodium phosphate, pH 7.0 solutions in H2O and D2O. In H2O, the decrease in the E0′ value is linear with increasing temperature up to 42°C. Above this temperature, the decrease is again linear but with a much greater slope. In D2O solutions, however, this biphasic behavior was not observed but instead a single line was obtained over the temperature range studied (25°C to 50°C). These results are interpreted in terms of the ability of NaCl to cause a destructuring of the bulk H2O above 42°C but not in the more stable D2O (Kreishman, Foss, Inoue and Leifer (1976) , 5431–5435). This decrease in water structure results in a shift in the equilibrium to the larger oxidized form as indicated by the decrease in E0′. 相似文献
2.
Temperature and light interact to modify the chemical and biochemical composition of a nitrogen-limited marine diatom, Thalassiosira allenii Takano, grown at a constant dilution rate in continuous culture and under a light:dark cycle.The percent of the total 14C incorporated into protein, polysaccharide and lipid, the N/C ratio and the C/cell varied with temperature in a markedly non-linear manner. The N/cell was negatively correlated to temperature. The Chl ratio was positively correlated with temperature under saturating light and non-saturating light for temperatures > 25 °C, but was constant under non-saturating light conditions for temperatures < 25 °C.Productivity index (PI) was negatively correlated to temperature under saturating light conditions, but did not vary under low light. In each case, the variation in PI with temperature was governed by the variation in Chl .The dark carbon loss rate was exponentially related to temperature and independent of light. Variation in the percent of the total 14C incorporated into protein and polysaccharide, the ratio and C/cell was primarily due to the effects of N-limitation < 20 °C and primarily due to the effects of temperature > 20 °C. Variation in N/cell was primarily due to the effects of temperature over the entire range of temperature studied. Variation in Chl was caused by the interaction of temperature and light effects.In most cases, temperature and nutrient effects interacted to govern how a particular parameter varied with temperature while light affected the range of values over which the parameter varied.The percent of the total 14C incorporated into protein exhibited a significant linear relationship with .The dark carbon loss rate, ratio and Chl ratio data were used to test the applicability of a model for the physiological adaptation of unicellular algae. The model, with parameters derived from a non-linear least-squares fit of the dark carbon loss rate data, adequately described the ratio between 15 and 25 °C at 290 and 137 μE · m?2 · s?1, but failed to describe the data at 28 °C and at 48 μE · m?2 · s?1. The Chl ratio was adequately described by the model under all light and temperature conditions. 相似文献
3.
Jørgen Vinten 《生物化学与生物物理学报:生物膜》1978,511(2):259-273
The transport of in white fat cells was measured under equilibrium exchange conditions at concentrations up to 50 mM with a previously described method (Vinten, J., Gliemann, J. and Østerlind, K. (1976) J. Biol. Chem. 251, 794–800). Under these conditions the main part of the transport was inhibitable by cytochalasin B. The inhibition was found to be of competitive type with an inhibition constant of about 2.5 · 10?7 M, both in the absence and in the presence of insulin (1μM). The cytochalasin B-insensitive part of the permeability was about 2 · 10?9 cm · s?1, and was not affected by insulin. As calculated from the maximum transport capacity, the half saturation constant and the volume/ surface ratio, the maximum permeability of the fat cell membrane to at 37°C and in the presence of insulin was 4.3 · 10?6 cm · s?1. From the temperature dependence of the maximum transport capacity in the interval 18–37°C and in the presence of insulin, an Arrhenius activation energy of was found. The corresponding value was in the absence of insulin. The half saturating concentration of was about 6 mM in the temperature interval used, and it was not affected by insulin, although this hormone increased the maximum transport capacity about ten-fold to 1.7 mmol · s?1 per 1 intracellular water at 37°C. 相似文献
4.
The association constant for the interaction of daunomycin with DNA was determined as a function of temperature (using [3H] daunomycin in conventional equilibrium dialysis cells) and ionic strength (using a spectrophotometric titration method). The association constant varied between 3.1 × 106 M?1 (4°C) and 3.9 × 105 M?1 (65°C). The free energy change was ?8.2 to ?8.8 , the enthalpy change ?5.3 and the entropy change +10 to +11 eu, all values being consistent with that expected of an intercalation process. The apparent number of intercalation sites detected (0.15 to 0.16 per nucleotide) was independent of temperature. The large positive entropy change accompanying the interaction appeals to be due to extensive release of water from the DNA and daunomycin. The apparent number of binding sites increased dramatically with decrease of ionic strength, although the apparent association constant remained largely unaffected by ionic strength. 相似文献
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6.
The temperature dependence of the binding of PhNapNH2 () to vesicles of egg phosphatidylcholine has been determined. The Arrhenius plot of the association constant exhibits a discontinuity at 20.9 °C, some 30 °C above the broad phase transition region of the phospholipid. In the temperature range above 20 °C, and ; in the temperature range below 20 °C, and These values are consistent with the view that there are well ordered lipid-lipid bonds below 20 °C which are significantly less important above this temperature. The order in the temperature range of 5 to 20 °C, though significantly greater than that above 20 °C, is still significantly less than that in the crystalline state. 相似文献
7.
Arrhenius diagrams of K+ pump fluxes measured between 15°C and 41°C were discontinuous in high K+ but not in low K+ sheep red cells. Exposure of low K+ cells to anti-L caused a bimodal temperature response of K+ pump flux with a transition temperature, , similar to that found in high K+ cells but with comparatively higher activation energies above . 相似文献
8.
Hemalatha Balaram B.V.Venkataram Prasad P. Balaram 《Biochemical and biophysical research communications》1982,109(3):825-831
The peptide t-butyloxycarbonyl-α-aminoisobutyryl-L-prolyl-L-prolyl-N-methylamide has been shown to adopt an extended structure in the solid state. The Pro-Pro segment occurs in the poly-proline II conformation. On dissolution of single crystals at ~ 233°K, a single species corresponding to the all peptide backbone is observed by 270 MHz 1H NMR. On warming, to isomerization about the Pro-Pro bond is facilitated. Both (ψ ~?50°) and (ψ ~ 130°) rotamers about the Pro3 CαCO bond are detectable in the Pro-Pro conformer, at low temperature. These observations demonstrate unambiguously the large differences in the solid state and solution conformations of a Pro-Pro sequence. 相似文献
9.
10.
Mahendra K. Jain Michael A. Singer Roger W. Crecely Hassan Pajouhesh Anthony J. Hancock 《生物化学与生物物理学报:生物膜》1984,774(2):199-205
In a previous publication, (Singer, M.A., Jain, M.K., Sable, H.Z., Pownall, H.H., Mantulin, W.W., Lister, M.D. and Hancock, A.J. (1983) Biochim. Biophys. Acta, 731, 373–377), we reported the properties of aqueous dispersions of the six diastereo-isomers of cyclopentanoid analogues of dipalmitoylphosphatidylcholine. Two of these isomers displayed unusually high enthalpies of transition, about double that of dipalmitoylphosphatidylcholine. One of the high enthalpy isomers whose configuration is all-trans has now been modified by the insertion of extra methylene residues ( through 9) between the nitrogen and phosphorus atoms of the headgroup. Vesicles were formed from these lipids and studied by 22Na permeability measurements, differential scanning calorimetry, fluorescence polarization, 31P-NMR, and freeze-fracture electron microscopy. Vesicles composed of lipids with or 3 exhibit a sharp transition at 46°C or 49°C, respectively, and a high enthalpy with no detectable sub- or pretransitions. Lipids with exhibit a main transition between 38 and 43°C with enthalpies and after prolonged cooling (more than 3 days at 4°C) a broad endotherm at about with enthalpies . These same dispersions display a permeability peak at 20–25°C and a second increase in 22Na efflux in the temperature range 30–40°C. The results of 31P-NMR measurements suggest that the acyl chains in 2,3-dipalmitoylcyclopentanol-phosphocholine () bilayers have restricted rotation below the main phase transition temperature. 相似文献
11.
The noise free 300 MHz 1H NMR spectra of β-DPN+, recorded in the Fourier mode at 12° and 68°C have been completely analysed by extensive computer simulation. It is shown, whether the coenzyme exists as an equilibrium mixture of folded ? extended forms (12°C) or in overwhelminghly extended forms (68°C), the backbone of both the nicotinamide and adenine fragments preferentially exist in conformation. This orientation is significantly different from those reported in the solid state for the extended species in contact with the enzyme where and orientations have been observed. It is suggested that specific interactions of the backbone with the various amino acid residues in the enzyme induces conformational aberrations in the backbone. Intimate details of the backbone conformation of the extended forms of AcPy-DPN+ and β-TPN+ are also presented. 相似文献
12.
The reaction of almond β-glucosidase with -nitrophenyl-β--glucoside has been investigated over the temperature range +25° to ?45° using 50% aqueous dimethyl sulfoxide (DMSO) as solvent. At temperatures below those at which turnover occurs a “burst” of -nitrophenol proportional to the enzyme concentration is observed. Such a “burst” suggests the existence of a glucosyl-enzyme intermediate whose breakdown is rate-limiting, and provides a method for measuring the active-site normality. At pH 5.9, 25°, the presence of 50% DMSO causes an increase in Km from 1.7×10?3M (0%) to 1.7×10?2M, whereas Vmax is unchanged. The DMSO thus apparently acts as a competitive inhibitor with Ki = 0.7M. The Arrhenius plot for turnover is linear over the accessible temperature range with Ea = 23.0 ± 2.0 kcal/mole. 相似文献
13.
The enthalpy of the helix-coil conversion of phenylalaninespecific transfer ribonucleic acid from brewer's yeast (tRNAPhebrewer's yeast) has been measured using both an LKB 10700-2 batch miciocalorimeter and an adiabatic differential scanning calorimeter. In the mixing calorimeter the conversion from coil to helix was induced by mixing a tRNAPhe solution with a solution containing an excess of MgSO4. We measured the enthalpy of this reaction stepwise in the temperature range from +9 to +60° C. For the enthalpy of folding of tRNAPhe from coil to helix this method yielded the remarkably high value of ?310 of tRNAPhe. With the differential scanning calorimeter in which the helix-coil conversion is simply induced by raising the temperature we found a value of +240 of tRNAPhe at a Tm value of 76° C and a value of +200 of tRNAPhe at a Tm value of 50° C. A comparison of the apparent van't Hoff enthalpies with the calorimetrically measured enthalpies shows, that the cooperativity of the system increases continually with rising melting temperatures - which are achieved by increasing Mg2+ concentrations - reaching a constant value at about 57° C. Above this temperature value the thermodynamic behaviour of the helix-coil conversion of tRNAPhe may be approximately described by the model of an all-or-none process. 相似文献
14.
We have studied the solid to liquid-crystalline phase transition of sonicated vesicles of dipalmitoylphosphatidylglycerol and dipalmitoylphosphatidylcholine. The transition was studied by both fluorescence polarization of perylene embedded in the vesicles, and by the efflux rate of trapped 22Na+.Fluorescence polarization generally decreases with temperature, showing an inflection in the region 32–42°C with a mid-point of approximately 37.5 °C. On the other hand, the perylene fluorescence intensity increases abruptly in this region. To explain this result, we have proposed that, for where is the transition temperature, perylene is excluded from the hydrocarbon interior of the membranes, whereas, this probe may be accommodated in the membrane interior to a large extent.The self-diffusion rates of 22Na+ through dipalmitoylphosphatidylglycerol vesicles exhibit a complex dependence on temperature. There is an initial large increase in diffusion rates (approximately 100-fold) between 30 and 38 °C, followed by a decrease (approximately 4-fold) between 38 and 48 °C. A monotonic increase is then observed at temperatures higher than 48 °C. The local maximum of 22Na+ self-diffusion rates at approximately 38 °C coincides with the mid-point of phase transition as detected by changes in fluorescence polarization of perylene with the same vesicles. Vesicles composed of dipalmitoylphosphatidylcholine show the same general behavior in terms of 22Na+ self-diffusion rates at different temperatures, except that the local maximum occurs at approximately 42 °C.The temperature dependence of the permeability and the appearance of a local maximum at the phase transition region could be explained in terms of a domain structure within the plane of the membranes. This explanation is based on the possibility that boundary regions between liquid and solid domains would exhibit relatively high permeability to 22Na+.Mixed vesicles composed of equimolar amounts of dipalmitoyl phospholipids and cholesterol show no abrupt changes in the temperature dependence of either perylene fluorescence polarization or 22Na+ diffusion rate measurements. This is taken to indicate the absence of agross phase transition in the presence of cholesterol. 相似文献
15.
D F Kimball L Peterson D J McLoughlin R G Wolfe 《Archives of biochemistry and biophysics》1979,195(1):66-73
Initial rate, product inhibition, and isotope rate kinetic studies of pig heart mitochondrial and supernatant malate dehydrogenases, acting upon the nonphysiological substrates, meso-tartrate and 2-keto-3-hydroxysuccinate, are reported. The measured spontaneous keto-enol equilibrium for 2-keto-3-hydroxysuccinate in 0.05 m Tris-acetate (pH 8.0) at 25 °C favors the enol form, dihydroxyfumarate, with an apparent equilibrium constant of 0.036. The enzyme-catalyzed reaction favors meso-tartrate with an apparent equilibrium constant of 1.25 × 10?6, M?1 at pH 8.0. The mechanism apparently remains ordered bi bi for both enzymes when these nonphysiological substrates are used, and the chemical-converting hydride transfer step becomes more rate limiting for both enzymes. This conclusion is supported by and values of 2.6 and 3.1, respectively, for the mitochondrial enzyme and 1.9 and 2.9, respectively, for the supernatant enzyme. 相似文献
16.
S. Subramaniun 《Biophysical chemistry》1978,7(4):375-378
The enthalpy change for the oxidative deamination of glutamate by NADP+ catalyzed by bovine liver glutamate dehydrogenase has been determined calorimetrically. The ΔHo values are 64.6 ± 1.2 and 70.3 ± 1.2 at 25 and 35°C respectively. The equilibrium constants for the reaction at the two temperatures were determined spectrophotometrically. This enabled the determination of ΔGo and ΔSo of the reaction as well. ΔHovalues were also determined for the reaction using an alternative coenzyme and the deuterated substrate. 相似文献
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18.
G W Pettigrew I Aviram A Schejter 《Biochemical and biophysical research communications》1976,68(3):807-813
Phage ?15 adsorbed at a low temperature (or by short-time incubation) to the outer surface of gathers on further incubation at a high temperature to a certain region where the inner and outer membranes may join. This was demonstrated by separating the inner and outer membranes of the cells in sucrose gradient after addition of 35S-labeled ?15 to the cells. Radioactivity adsorbed at 4° was first recovered mainly with the dense outer membrane but disappeared by further incubation at 35° within 5 min. Instead, the radioactivity was recovered with the membrane fraction which had intermediate density. Such phage translocation was not observed when phage ?15 was added to a to which the phage can adsorb but fail to infect. A host range mutant phage which can infect the mutant migrated to the intermediate dense region. 相似文献
19.
Pharmacological properties of imidazole. 2. Action on the normal body temperature regulation in rats
Rats injected intraperitoneally with imidazole (100 to 400 mg/kg) showed a progressive dose-dependent decrease in rectal temperature. A decrease of 6C occurred when the imidazole-treated animals were placed in a 4C environment. In a 23C environment, the rectal temperature declined about 2C. The results show that imidazole induces a decline in body temperature in non-febrile rats, possibly due to an action on hipothalamic calcium levels. 相似文献
20.
The thermoelectric (Seebeck) coefficient () in various cuticular areas of the Oriental hornet (Vespa orientalis) fluctuates from 0·3 to 2·4 mV deg?1 within a temperature range of 27–36°C and when the temperature difference between the two measuring electrodes (ΔT) is 0·6–8·0°C. The values measured on the brown-colored cuticle suggest an n-type conduction, while those measured on the yellow-colored cuticle point to a p-type conduction. It is suggested hornets use this phenomenon for temperature detection. 相似文献