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21.
Helix–coil transition of poly(γ-methyl-L -glutamate), poly(γ-ethyl-L -glutamate), and poly(γ-benzyl-L -glutamate) has been studied in mixed solvents by calorimetry, polarimetry, and viscometry. The experimental data have allowed the evaluation of solvation enthalpy Δhb, equilibrium constant K for hydrogen bond formation between the active solvent component and CO and NH groups, and the cooperativity parameter σ. The conformational transition of polypeptides in solution in a mixed solvent containing enough active solvent to maintain the coiled conformation has been produced by dilution with the helix-supporting solvent for the measurements of enthalpy of transition Δhs. The average value for Δhs is 3550 ± 300 J/mol and is practically independent of the nature of the side chain for the dichloroacetic acid-ethylene dichloride solvent pair at 25°C. A noticeable concentration effect exists in the case of poly(γ-benzyl-L -glutamate). The helical conformation is less stable for poly(γ-ethyl-L -glutamate), and this is explained by a steric effect hindering the access of dichloroacetic acid to side chains. Constant K has been calculated using polarimetric data and also from values of Δhs obtained at different temperatures using the Bixon and Lifson theory on the one hand and that of Sayama and coworkers on the other hand. Values of σ for poly(γ-ethyl-L -glutamate) have been calculated according to both theories mentioned, and the results show that the two sets of values are quite similar. The constant σ depends on the nature of the active solvent, on temperature, and on the binary-solvent composition. These conclusions are confirmed by viscometric results. Values of Δhb calculated from constant K are 5230 J/mol when Bixon and Lifson theory is used and 5569 J/mol when the theory at Sayama and coworkers is used. In both cases the value for Δhb is much lower than that of an intramolecular hydrogen bond. Experimental results suggest that the solvation mechanism would proceed in a manner so that mechanisms described in both theories are involved. 相似文献
22.
23.
Hubert Schwabl Eberhard Gwinner Silvano Benvenuti Paolo Ioal 《Ethology : formerly Zeitschrift fur Tierpsychologie》1991,88(1):35-45
We caught dunnocks at a wintering site near Pisa/Italy prior to their departure for breeding territories and held them indoors north of this site (Andechs/Germany) on a simulated photoperiod of 52.5 °N. After birds had gone through a reproductive cycle and postnuptial moult they developed migratory restlessness in autumn. At this time one group was transferred back to the previous wintering site (Pisa) where birds were held in individual activity cages in an outdoor aviary, allowing them to perceive as much environmental information as possible. A second group was transferred to a control site near Tour du Valat/France of approximately the same latitude and climate, but different longitude and held in an identical aviary. The diurnal activity pattern changed after transfer back to the previous wintering site, but not after transfer to the control site. Specifically, the amount of morning activity was reduced while afternoon activity was increased. This effect was restricted to those individuals that had been developing nocturnal migratory restlessness the previous spring. It was absent in individuals without migratory restlessness in spring, indicating that the different patterns were not due to unspecific effects from the testing sites. These results are consistent with the hypothesis that birds were able to derive information about their locality and to recognize their previous wintering site, resulting in suppression of migratory state by experience. The results are not definitely conclusive, however, because of several difficulties in the interpretation of perch-hopping activity, which are discussed in detail. 相似文献
24.
Summary The regulation of extracellular amylase production by the basidiomycetous yeast Filobasidium capsuligenum CCY 64-5-1 was characterized using growing and resting cells. A basal level of amylolytic activity was produced with various carbon sources including glucose. Amylase secretion was repressed by glucose and, more severely, by 2-deoxy-d-glucose, whereas compounds with -1,4-linked glucose, such as methyl glucoside, maltose, -cyclodextrin and soluble starch, served as inducers. Repression was not relieved by exogenously added cAMP. The effects of several metabolic inhibitors on amylase secretion were studied. Following UV-mutagenesis a mutant strain (FC-5) capable of growing in a 2-deoxy-d-glucose supplemented corn starch medium was selected for further characterization. This strain produced more amylase, had acquired an increased resistance against repression by glucose, and retained a growth rate comparable to the wild type. FC-5 was also characterized by a reduced glucokinase activity and an increased hexokinase activity. 相似文献
25.
By means of pH-sensitive microelectrodes, cytoplasmic pH has been monitored continuously during amino-acid transport across the plasmalemma of Riccia fluitans rhizoid cells under various experimental conditions. (i) Contrary to the general assumption that import of amino acids (or hexoses) together with protons should lead to cytoplasmic acidification, an alkalinization of 0.1–0.3 pHc units was found for all amino acids tested. Similar alkalinizations were recorded in the presence of hexoses and methylamine. No alkalinization occurred when the substrates were added in the depolarized state or in the presence of cyanide, where the electrogenic H+-pump is inhibited. (ii) After acidification of the cytoplasm by means of various concentrations of acetic acid, amino-acid transport is massively altered, although the protonmotive force remained essentially constant. It is suggested that H+-cotransport is energetically interconnected with the proton-export pump which is stimulated by the amino-acid-induced depolarization, thus causing proton depletion of the cytoplasm. It is concluded that, in order to investigate H+-dependent cotransport processes, the cytoplasmic pH must be measured and be under continuous experimental control; secondly, neither pH nor the protonmotive force across a membrane are reliable quantities for analysing a proton-dependent process.Abbreviations 3-OMG
3-oxymethylglucose
- pHc
cytoplasmic pH
-
m
electrical potential difference across the respective membrane, i.e. membrane potential
- H+/F (=pmf)
electrochemical proton gradient 相似文献
26.
Nicolas Mermod Juan L. Ramos Amos Bairoch Kenneth N. Timmis 《Molecular & general genetics : MGG》1987,207(2-3):349-354
27.
C Junien J Boué C Duros M Coulon P Cohen I Dehaupas P Gallano B Léotard H Nicolas A Boué 《Annales de génétique》1987,30(1):5-16
Carrier diagnosis and prenatal diagnosis of Duchenne's muscular dystrophy (DMD) and Becker's muscular dystrophy (BMD) has become possible using some twenty RFLPs detected by more than a dozen Xp21 probes that are either intragenic or flanking the disease locus. Results from familial studies on 88 DMD and BM families stress important considerations concerning a priori and final risks, individuals necessary for the identification of the phase, and the different strategies that can be applied, regardless of whether the study concerns an on-going pregnancy or a carrier-status determination, and whether the patient is at high or low risk. Finally, multiple sources of difficulties in interpreting the results depend on a) the occurrence of new mutations that must be traced; b) the existence of meiotic recombination; c) the necessity, in some instances, of relying upon the sole identification of the paternal X. These considerations emphasize the characteristics and the important limitations of this type of methodology. 相似文献
28.
Dr. Hansjörg Wunderer Serge Picaud Nicolas Franceschini 《Cell and tissue research》1989,257(3):565-576
Summary Single photoreceptor cells in the compound eye of the housefly Musca domestica were selectively illuminated and subsequently compared electron-microscopically with the unilluminated photoreceptors in the immediate surroundings. The rhabdomeres of the illuminated cells remain largely unaffected, but the cells show an increase in the number of coated pits, various types of vesicles, and degradative organelles; some of the latter organelles are described for the first time in fly photoreceptors. Coated pits are found not only at the bases of the microvilli, but also in other parts of the plasma membrane. Degradative organelles, endoplasmic reticulum (ER) and mitochondria aggregate in the perinuclear region. The rough ER and smooth ER are more elaborate, the number of Golgi stacks, free ribosomes and polysomes is increased, and the shape and distribution of heterochromatin within the nuclei are altered. Illuminated photoreceptors also interdigitate extensively with their neighbouring secondary pigment cells. These structural changes in illuminated fly photoreceptor cells indicate an increase in membrane turnover and cellular metabolism. When applied to the eye, Lucifer Yellow spreads into the extracellular space and is taken up only by the illuminated photoreceptor cells. These cells show the same structural modifications as above. Horseradish peroxidase applied in the same way is observed in pinocytotic vesicles and degradative organelles of the illuminated cells. Hence, the light-induced uptake of extracellular compounds takes place in vivo at least partially as a result of an increase in pinocytosis. 相似文献
29.
Perturbations induced by a toxic lectin (ricin) on lipid organisation of model membranes prepared with DPPC and DPPC-cerebrosides mixtures have been analysed by Raman and infrared spectroscopy, two powerful and non-invasive methods. Our approach involves the observation of changes in the vibrational spectra of liquid multilayers in the PO
2
-
, C=0 and CH2 spectral regions for two lipid: ricin molar ratios (225:1, 75:1).The interfacial and polar regions of the multilayers, analysed by FTIR, appear to be perturbed by the protein. With both kinds of membranes, ricin mainly perturbs the C=0 ester groups of the sn-2 acylchain of DPPC. In the PO
2
-
stretching region, the frequency shifts are correlated with changes in polar group hydration.In the hydrophobic core of the multilayer membrane studied by Raman spectroscopy, the interaction of ricin is associated with changes in lipid packing. These perturbations depend upon the lipid composition of the membrane. With DPPC membranes, an affect is detected at temperatures lower than T
m
.It corresponds to a decrease of the lipid ordering. With DPPC-cer membranes, the protein increases the acylchain packing order regardless of the temperature of the experiments (10°C<T<75°C). No perturbation of T
m
is observed after addition of ricin to either DPPC or DPPC-cer membranes.The different perturbations detected by Raman and FTIR suggest that ricin mainly interacts with the interfacial domains of the membranes. 相似文献
30.
Teresa Urbanik-Sypniewska Ulrich Seydel Michaela Greck Jürgen Weckesser Hubert Mayer 《Archives of microbiology》1989,152(6):527-532
The structure of the lipopolysaccharide from Rhizobium meliloti 10406, a derivative of the wild-type strain MVII-1, was examined. The compositional analysis of its polysaccharide moiety demonstrated lack of heptose(s), but high contents in glucose, galacturonic acid and 2-keto-3-deoxy-octonate (dOclA) as characteristic features. The lipid A moiety consisted of a -1,6 linked glucosamine disaccharide carrying ester (at C-4) and glycosidically (at C-1) linked phosphate residues, both present exclusively as monoester phosphates but not as phosphodiesters. Ester- and amidelinked 3-hydroxy fatty acids were mostly present as non-3-O-acylated residues. Laser desorption mass spectrometry (LD-MS) revealed heterogeneity in the fatty acid substitution, as was also indicated by the non-stoichiometric ratios obtained by quantitative fatty acid analysis. The predominating lipid A structure contained at the reducing glucosamine residue ester-linked 3-hydroxy-tetradecanoic acid (3-OH-14:0) and amide-linked 3-OH-18:0, or 3-OH-18:1, respectively. The distal (non-reducing) glucosamine carried ester-bound the recently discovered 27-hydroxyoctacosanoic acid and 3-OH-14:0 and, as amide-linked fatty acid, mostly 3-hydroxy-stearic acid (3-OH-18:0).The isolated lipopolysaccharide exhibited a high extent of lethal toxicity in galactosamine-treated mice, comparable to that of enterobacterial lipopolysaccharide. The structural relationship of LPS and lipid A of Rhizobium meliloti to other rhizobial lipopolysaccharides and lipid A's with respect to questions of taxonomy and of phylogenetic relationships will be discussed.Abbreviations LPS
lipopolysaccharide
- dOclA
3-deoxy-D-mannooctulosonic acid (KDO)
- GalA
galacturonic acid
- DOC
sodium deoxycholate
- PAGE
polyacrylamide gel electrophoresis
- LD-MS
laser desorption-mass spectrometry 相似文献