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1.
Isolation and preliminary characterization of Pichia pinus mutants insensitive to glucose repression
A new method for the isolation of glucose repression-insensitive mutants in the methylotrophic yeast Pichia pinus was developed. The method is based on screening of small suspension samples derived from 2-deoxyglucose-resistant colonies for alcohol oxidase activity. Alcohol oxidase activity was evaluated by determination of formaldehyde excreted by cells. Mutants with glucose non-repressible alcohol oxidase and catalase synthesis were obtained. All mutants grew poorly on D -xylose compared to the wild type, whereas growth on L -arabinose was similar to the wild type. Changes in the glucose transport system were suggested to be responsible for altered growth characteristics and defective glucose repression. 相似文献
2.
Measurements of relaxation times, T1 and T2, and self-diffusion coefficients, D, for small molecules, viz., H2O, dioxane and t-butanol, in the gel system cellulose/H2O are reported and compared with those for H2O in a polyacrylamide gel of the same polymer content. The temperature dependence of T1 and D can for all the penetrants be represented by Arrhenius type relations which merely are parallel shifts by the same amount, towards smaller values, of those obtained without polymer. The T2 values for H2O in both gels pass through a shallow minimum over the considered temperature interval (14°?44°C). Furthermore, relaxation times T1 of D2O in the gel system cellulose/D2O are reported; in a plot of ln T1 vs. 1/T, a plateau region is observed at higher temperatures. 相似文献
3.
In this paper, we present the systematic development of mechanically enhanced interpenetrating polymer network (IPN) hydrogels with Young's moduli rivaling those of natural load-bearing tissues. The IPNs were formed by synthesis of a crosslinked poly(acrylic acid) (PAA) network within an end-linked poly(ethylene glycol) (PEG) macromonomer network. The strain-hardening behavior of these PEG/PAA IPNs was studied through uniaxial tensile testing and swelling measurements. The interaction between the independently crosslinked networks within the IPN was varied by (1) changing the molecular weight of the PEG macromonomer, (2) controlling the degree of PAA ionization by changing pH, and (3) increasing the polymer content in the PAA network. Young's moduli and the maximum stress-at-break of the swollen hydrogels were normalized on the basis of their polymer content. Strain hardening in the IPNs exhibited a strong dependence on the molecular weight of the first network macromonomer, the pH of the swelling buffer, as well as the polymer content of the second network. The results indicate that the mechanical enhancement of these IPNs is mediated by the strain-induced intensity of physical entanglements between the two networks. The strain can be applied either by mechanical deformation or by changing the pH to modulate the swelling of the PAA network. At pHs below the pKa of PAA (4.7), entanglements between PEG and PAA are reinforced by interpolymer hydrogen bonds, yielding IPNs with high fracture strength. At pHs above 4.7, a “pre-stressed” IPN with dramatically enhanced modulus is formed due to ionization-induced swelling of the PAA network within a static PEG network. The modulus enhancement ranged from two-fold to over 10-fold depending on the synthesis conditions used. Variation of the network parameters and swelling conditions enabled “tuning” of the hydrogels' physical properties, yielding materials with water content between 58% and 90% water, tensile strength between 2.0 MPa and 12.0 MPa, and initial Young's modulus between 1.0 MPa and 19.0 MPa. Under physiologic pH and salt concentration, these materials attain “biomimetic” values for initial Young's modulus in addition to high tensile strength and water content. As such, they are promising new candidates for artificial replacement of natural tissues such as the cornea, cartilage, and other load-bearing structures. 相似文献
4.
The effect of the reaction temperature and the metals of an iron subgroup on the thermo-chemical treatment of titanium carbide with a chlorine gas and their influence on the carbon structure obtained thereby was studied. Different analytical methods such as porosity measurements, X-ray diffraction spectrometry and a high-resolution electron microscopy revealed the catalytic behaviour of the above-mentioned metals, which appeared to support the formation of graphitised carbon at much lower temperatures compared to those needed for the ordinary thermo-chemical chlorination of titanium carbide. 相似文献
5.
Lipid and fatty acyl composition of rat brain capillary endothelia isolated by a new technique 总被引:7,自引:0,他引:7
A method is described for the isolation of pure capillary endothelia from rat brain and the phospholipid composition of these
cells is reported. This method is rapid and requires only a small amount of starting material. It involves: (a) tissue disruption
by high speed homogenization, (b) separation of the capillary endothelia from other brain structures using sucrose gradients,
and (c) a final purification using a glass bead column. Choline and ethanolamine phosphoglycerides were found to be the predominant
lipid classes of these cells amounting to 31.9% and 24.4%, respectively, of total phospholipids. The choline phosphoglycerides
consisted almost exclusively of 1,2-diacyl glycerophosphorylcholine, whereas the ethanolamine phosphoglycerides consisted
of approximately equal amounts of 1,2-diacyl and 1-alk-l’-enyl-2-acyl glycerophosphorylethanolamine. The composition of the
constituent fatty acids of both choline and ethanolamine phosphoglycerides and the alk-1-enyl composition of ethanolamine
phosphoglycerides is reported. Saturated fatty acids accounted for 45% of the total fatty acids in choline phosphoglycerides
and for 53% in ethanolamine phosphoglycerides. Arachidonic acid accounted for approximately 48% of the total fatty acids in
alk-1-enyl ethanolamine phosphoglyceride. 相似文献
6.
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8.
The electrophysiological properties of the Na+/I- symporter (NIS) were examined in a cloned rat thyroid cell line (FRTL-5) using the whole-cell patch-clamp technique. When the holding potential was between -40 mV and -80 mV, 1 mM NaI and NaSCN induced an immediate inward current which was greater with SCN- than with I-. The reversal potential for I- and SCN- induced membrane currents was +50 mV. This is close to the value of +55 mV calculated by the Nernst equation for Na+. These results are consistent with I- and SCN- translocation via the NIS that is energized by the electrochemical gradient of Na+ and coupled to the transport of two or more Na+. There was no change in the membrane current recording with ClO-4 indicating that ClO-4 was either not transported into the cell, or the translocation was electroneutral. ClO-4 addition, however, did reverse the inward currents induced by I- or SCN-. These effects of I-, SCN- and ClO-4 on membrane currents reflect endogenous NIS activity since the responses duplicated those seen in CHO cells transfected with NIS. There were additional currents elicited by SCN- in FRTL-5 cells under certain conditions. For example at holding potentials of 0 and +30 mV, 1 mM SCN- produced an increasingly greater outward current. This outward current was transient. In addition, when SCN- was washed off the cells a transient inward current was detected. Unlike SCN-, 1-10 mM I- had no observable effect on the membrane current at holding potentials of 0 and +30 mV. The results indicate FRTL-5 cells may have a specific SCN- translocation system in addition to the SCN- translocation by the I- porter. Differences demonstrated in current response may explain some of the complicated influx and efflux properties of I-, SCN- and ClO-4 in thyroid cells. 相似文献
9.
Malle Mandre Henn Pärn Jaan Klõšeiko Morten Ingerslev Inge Stupak Margus Kört Keddy Paasrand 《Biomass & bioenergy》2010,34(9):1384-1392
Short-term effects of different doses (0.25; 0.5 and 1.0 kg m?2) of wood ash (WA), peat ash (PA) and their mixture (MA) applied to peat substrate on the mineral composition and growth of seedlings of Betula pendula were investigated. The experiments were conducted with 1-year-old seedlings planted in vegetation pots. The pH of the substrate was increased by 0.4–0.9 units during the vegetation period compared to the control. The peat substrate was poor in nutrients, except N. The substrate treated with WA had higher concentrations of K, Mg, Mn, Fe, P, Zn, Cr and Pb, but a lower N concentration compared to the control. The substrate treated with PA had higher concentrations of Ca, Mg, N and P. The concentrations in the MA treatment were intermediate between WA and PA. The ashes increased K and lowered the concentration of Ca. A decrease in N in seedlings was found under the influence of WA and MA. An increase in K and P was found in all compartments of seedlings, while the concentrations of Ca, Mg, Cu, Zn, Cd and Cr in seedlings were affected irregularly depending on types and doses of ashes used. The uptake of Cd, Cr and Pb did not reach phytotoxic levels; however, increased concentrations of Cd and Pb were found in roots. A positive influence of ash application on growth was found. The heights and root collar diameters of all ash-fertilised treatments exceeded those of the control seedlings in most cases. 相似文献
10.
Raoudha Haddad Michael Holzinger Reynaldo Villalonga Astrid Neumann Jaan Roots A. Maaref Serge Cosnier 《Carbon》2011,(7):2571-2578
The design of nanostructured biological architectures based on host–guest interactions between β-cyclodextrin and adamantane was investigated on SWCNT coatings using glucose oxidase (GOX) as biomolecule model. β-Cyclodextrin tagged GOX was immobilized on adamantane functionalized carbon nanotubes, deposited on platinum electrodes. Different functionalization techniques to attach “pyrene adamantane” on nanotubes were studied and compared in terms of the performances of the subsequently constructed glucose biosensors. The best results were obtained by dipping the nanotube deposit into a pyrene-adamantane solution followed by electropolymerization of the adsorbed pyrene monolayer. The constructed biosensor exhibited a good linear response toward glucose concentrations between 2 × 10−7 M and 1.6 × 10−3 M. The maximum current density and glucose sensitivity were 154.9 μA cm−2 and 14.4 mA M−1 cm−2, respectively. 相似文献