共查询到20条相似文献,搜索用时 15 毫秒
1.
B.M. Fung James L. McAdams 《Biochimica et Biophysica Acta (BBA)/General Subjects》1976,451(1):313-320
2H and 31P spin-lattice relaxation times (T1) were studied for invented egg phosphatidylcholine micelles in CCl4 as functions of 2H2O concentration. When the 2H2O/phosphatidylcholine mole ratio changed from 1.0 to 18.0, T1 of 31P increased by about 2.6 fold, whereas T1 of 2H increased by about 50 fold. A quantitative analysis of the deuterium T1 data showed that there is only one water molecule tightly bound to the polar head, and it is in rapid exchange with the rest of the water molecules. The activation energy for the deuterium T1 was 7.1 ± 0.8 kcal/mol (30 ± 3 kJ/mol), and was independent of the 2H2O concentration. 相似文献
2.
Toru Shimizu Masato Kodaka Masahiro Hatano 《Biochemical and biophysical research communications》1982,106(3):988-993
67Zn NMR studies of naturally abundant Zn2+-imidazole and carboxylate ligands Complexes are shown. Thus, quadrupolar relaxation changes in 67Zn NMR caused by adding imidazole ligands are more remarkable than those by carboxylate ligands. The changes caused by adding less bulky imidazole ligands are more prominent than those caused by a bulky imidazole ligan. Changes in Zn2+ quadrupolar relaxation rate caused by adding a cyclic hexapeptide consisting of L-histidine, L-cystein(Acm) and D-leucine are larger than those by a corresponding linear hexapeptide. Those changes in the quadrupolar relaxation rate of 67Zn NMR among Zn2+ complexes can be reasonably interpreted in terms of the differences of equilibrium constants of those complexes to a first approximation. 相似文献
3.
Moshe Rehavi Yitzhak Ittah Kenner C. Rice Phil Skolnick Frederick K. Goodwin Steven M. Paul 《Biochemical and biophysical research communications》1981,99(3):954-959
The effect(s) of a new imipramine analogue, 2-nitroimipramine, on high affinity [3H] imipramine binding and [3H] serotonin uptake in human platelets were studied. 2-Nitroimipramine was found not only to be a very potent inhibitor of [3H] imipramine binding and [3H] serotonin uptake but was found to irreversibly inhibit binding and uptake simultaneously. This finding supports previous observations from our laboratory and others that high affinity imipramine binding labels serotonin uptake or transport sites. 2-Nitroimipramine should prove an important tool for subsequent studies of the molecular mechanism(s) involved in the transport of serotonin and the binding of imipramine to platelet and brain membranes. 相似文献
4.
Haggai Gilboa Assaf Steinschneider Bill Valentine Devindra Dhawan Daniel Fiat 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,800(3):251-257
17ONMR measurements of labeled Pro-Leu-Gly-NH2 were carried out at different pH levels and in mixed solvents of water/acetonitrile. Complementary studies of the amide protons were carried out in acetonitrile-d3. Only the prolyl group was sensitive to the pH level. Protonation of the amine group resulted in an upfield chemical shift of 18 ppm. The chemical shifts of each of the three oxygen sites was sensitive to the ratio water: acetonitrile. Solvent composition dependence of the chemical shift and linewidth suggests that the prolyl is involved in intramolecular hydrogen bond formation when Pro-Leu-Gly-NH2 is dissolved in acetonitrile, while in water there is no intramolecular H bond. 相似文献
5.
The interaction between the plant hormone, 3-indoleacetic acid (IAA), and some phospholipids in CDCL3 has been studied by 1H, 13C and 31P nuclear magnetic resonance (NMR) spectroscopy. Upon interaction with IAA, significant changes occurred in resonance positions of the phospholipid head group nuclei. Alteration of the fatty acid composition influenced the effects of IAA on these nuclei. These effects were observed in the ethanolamine and phosphate groups of the phosphatidylethanolamines, and in the choline, phosphate and glycerol groups of the phosphatidylcholines. Changes in resonance positions of the phospholipid head group nuclei were used for the determination of dissociation constants (Kd). In all cases, Kd values were approx. 10?2 molal for 1 : 1 interaction. The NMR results suggest an interaction orientation in which the aromatic ring system of IAA interacts with the quaternary nitrogen function of the head group, and the phosphate group becomes hydrogen-bonded to the NH or carboxyl proton of 1AA. 相似文献
6.
D.M. Wilson A.L. Burlingame T. Cronholm J. Sjövall 《Biochemical and biophysical research communications》1974,56(3):828-835
[1-13C, 1,1-2H2] ethanol and [2,2,2-2H3] ethanol were administered to bile fistula rats. A new technique, 2H, 1H-decoupled 13C nuclear magnetic resonance, was used in attempting to account for the distribution of the isotopic species along the steroid skeleton of 3–45 mg of isolated bile acids. The technique revealed 2H incorporation at many carbon sites unambiguously, but has limitations as a quantitative 2H assay at these levels of sample availability. 相似文献
7.
8.
The mitochondrial fraction of diethylstilbestrol-treated rat uteri, known to contain an estrogen-induced peroxidase, was able to catalyze the release of 3H2O from either [2-3H]- or [4-3H]estradiol. Hydrogen peroxide added to this system increased the yield of 3H2O but had no effect on mitochondrial preparations from ovariectomized rat uteri having only very low peroxidase activity. The reaction was inhibited by catalase and also occurred with lactoperoxidase in the presence of H2O2 but 2-hydroxyestradiol was not detected in any of these experiments. Under similar conditions, tyrosinase catalyzed the formation of the catechol estrogen with loss of 3H from [2-3H]- or [2,4,6,7-3H]- but not [4-3H]- or [6,7-3H]estradiol. It is proposed that the formation of 3H2O from 3H-labeled estradiol in the estrogen-treated rat uterus may occur by a peroxidative mechanism which does not necessarily result in hydroxylation of the steroid. 相似文献
9.
Lyophilized purple membrane sheets have been investigated by C-13- and P-31-cross polarization/magic angle spinning N M R spectroscopy. The high-resolution C-13 spectrum and its non-quaternary suppression version indicate fast protein side-chain motions but a rigid backbone structure on a time scale of roughly < 0.001 to 0.01 s. Three components of exchangeable hydrogen have been detected by deuterium N M R. The mean exchange time of the peptide hydrogens must be longer than 1 μs. The medium component is attributed to mobile side-chains. In addition a narrow line has been observed which is assigned to the residual hydration water. 相似文献
10.
The anomeric composition and mutarotation rates of fructose 1,6-bisphosphate were determined in the presence of 100 mm KCl at pH 7.0 by 31P NMR. At 23 and 37 °C the solution contains (15 ± 1)% of the α anomer. The anomeric rate constants at 37 °C are (4.2 ± 0.4) s?1 for the β → α anomerization and (14.9 ± 0.5) s?1 for the reverse reaction. A D2O effect between 2.1 and 2.6 was found. From acid base titration curves it appeared that the pK values of the phosphate groups range from 5.8 to 6.0. Mg2+ and Zn2+ bind preferentially to the 1-phosphate in the α-anomeric position. Zn2+ has a higher affinity for this phosphate group than Mg2+ has. At increasing pH the fraction α anomer decreases slightly. At increasing Mg2+/fructose 1,6-bisphosphate ratios the fraction α anomer increases till 19% at a ratio of 20. Proton and probably Mg2+ binding decreases the anomerization rate. The time-averaged preferred orientation of the 1-phosphate along the C1O1 bond of the α conformer is strongly pH dependent, gauche rotamers being predominant at pH 9.4. In the presence of divalent cations the orientation is biased toward trans. A mechanistic model is proposed to explain the Zn2+, Mg2+, and pH-dependent behavior of the gluconeogenic enzyme fructose 1,6-bisphosphatase. 相似文献
11.
12.
Marc Lecouvey Céline Frochot Laurent Miclo Piotr Orlewski Michel Marraud Jean-Luc Gaillard Manh Thong Cung Régis Vanderesse 《Letters in Peptide Science》1997,4(4-6):359-364
The conformation of a benzodiazepine-like decapeptide corresponding tothe YLGYLEQLLR fragment of a casein has been examined in a sodium dodecylsulfate micellar medium using circular dichroism, two-dimensional1H NMR spectroscopy and restrained molecular dynamicssimulation. The decapeptide adopts an amphipathic 310-helicoidstructure in which theE6···R10 ionic bridgestabilizes the C-terminus. 相似文献
13.
The high resolution 1H and 13C nuclear magnetic resonance (NMR) spectra of galactosylceramides containing n-fatty acids and α-hydroxy fatty acids were recorded in dimethylsulfoxide solution with and without addition of D2O. From the coupling constants of the sugar ring protons, a 4C1 conformation can be deduced. In contrast to the conformation in aqueous solution, the C6 hydroxymethylene group is freely rotating around the C6C5 bond. In the ceramide residue all signals produced by protons linked to carbons bearing electronegative substituents could be attributed. The large difference in coupling constants of the methylene protons of C1′ to the C2′ methine proton of the sphingosine indicates a restricted rotation around the C1′C2′ bond. The assignments of the hydroxy and amino protons follow from the decoupling of the corresponding methine protons. 相似文献
14.
Characterization of temperature-sensitive [3H]serotonin (5-HT) binding sites (1 and 4 nM Kd sites) revealed complex inhibition by neuroleptics and serotonin antagonists. There was no simple correlation with affinities for S1 and S2 receptors. pretreatment (48 h before) with mianserin did not alter Bmax or Kd for the 1 nM Kd [3H]5-HT site, although [3H]ketanserin (S2) densities were decreased by 50%. This suggested that possible S2 components of [3H]5-HT binding must be negligeable, even though ketanserin competed with high affinity (IC50 = 3 nM) for a portion of the 1 nM Kd [3H]5-HT site. Low concentrations of mianserin inhibited the 1 nM Kd [3H]5-HT site in a non-competitive manner, as shown by a decrease in Bmax with no change in Kd after incubation. The complex inhibition data may therefore represent indirect interactions through another site. 相似文献
15.
A molecular dynamics investigation and coarse-grained analysis of inactivated actin-related protein (Arp) 2/3 complex is presented. It was found that the nucleotide binding site within Arp3 remained in a closed position with bound ATP or ADP, but opened when simulation with no nucleotide was performed. In contrast, simulation of the isolated Arp3 subunit with bound ATP, showed a fast opening of the nucleotide binding cleft. A homology model for the missing subdomains 1 and 2 of Arp2 was constructed, and it was also found that the Arp2 binding cleft remained closed with bound nucleotide. Within the nucleotide binding cleft a distinct opening and closing period of 10 ns was observed in many of the simulations of Arp2/3 as well as isolated Arp3. Substitution studies were employed, and several alanine substitutions were found to induce a partial opening of the ATP binding cleft in Arp3 and Arp2, whereas only a single substitution was found to induce opening of the ADP binding cleft. It was also found that the nucleotide type did not cause a substantial change on interfacial contacts between Arp3 and the ArpC2, ArpC3 and ArpC4 subunits. Nucleotide-free Arp3 had generally less stable contacts, but the overall contact architecture was constant. Finally, nucleotide-dependent coarse-grained models for Arp3 are developed that serve to further highlight the structural differences induced in Arp3 by nucleotide hydrolysis. 相似文献
16.
Bogdan E. Chapman Georg R. Beilharz Michael J. York Philip W. Kuchel 《Biochemical and biophysical research communications》1982,105(4):1280-1287
1H spin-echo NMR spectroscopy has been used to show for the first time, to our knowledge, the presence of a phospholipase D activity in human erythrocytes. The enzyme is presumably intra-cellular and we have demonstrated that it is activated by a component of Krebs bicarbonate medium; most probably calcium ions. The existence of a phospholipase in human erythrocytes allows a simple explanation for the choline accumulation that occurs in these cells of manic-depressive and other patients receiving lithium carbonate therapy. 相似文献
17.
When 32Pi-labeled rabbit platelets were incubated with 5 × 10?10m 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (AGEPC), either in the presence or absence (0.1 mm EGTA) of added Ca2+, there was a three- to five-fold increase in the [32P]phosphatidic acid (PA) pool within 15 to 20 s. This event was followed by a gradual decrease in the [32P]PA level to near basal level in 5 min. AGEPC effected this change in [32P]PA in a characteristic dose- and time-dependent manner. Polar head group analogs of AGEPC, such as AGEDME and AGEMME, also effected an increase in PA labeling at levels. comparable to those previously reported for their activity toward rabbit platelets [K. Satouchi, R. N. Pinckard, L. M., McManus, and D. J. Hanahan (1981) J. Biol. Chem.256, 4425–4432]. Other analogs, i.e., lysoGEPC and the enantiomer, sn-1-AGEPC, which are inactive toward rabbit platelets, also showed no effect on the level of [32P]PA. The finding that the PA level in rabbit platelets could be manipulated by the addition of AGEPC, without any added Ca2+, provided an excellent model system for establishinig a correlation between the uptake of Ca2+, serotonin release, and PA level. Thus, PA must be regarded as a sensitive indicator of a reaction mechanism important to the platelet response to AGEPC, and could be the focal point in promoting calcium uptake during the stimulation process. 相似文献
18.
Yitzhak Koch Fiorenzo Battaini Alan Peterkofsky 《Biochemical and biophysical research communications》1982,104(2):823-829
Cyclo(Histidyl-Proline), a metabolite of TRH, has been demonstrated to have a number of biological activities. The clearance, distribution and binding of the peptide in the rat was studied. Cyclo(His-Pro) was cleared from the circulation biphasically (). Unmetabolized cyclo(His-Pro) appeared rapidly in urine. Accumulation of [3H]cyclo(His-Pro) in adrenal, liver and kidney was demonstrated. Membrane preparations from adrenal and liver, but not from kidney, brain, pituitary, and other tissues were shown to bind cyclo(His-Pro) specifically. 相似文献
19.
The interactions of putative mu and delta selective ligands with [3H]D-ala2-D-leu5 enkephalin (DADLE) binding to mouse brain membranes were investigated. Computerized curve fitting of displacement curves performed at three different concentrations of 3H-DADLE indicated that a one site competitive model was sufficient to explain the interactions of leu-enkephalin (LE) and D-ser2-thr6-leucine enkephalin with 3H-DADLE binding. Similar experiments with morphine and morphiceptin were unique in that the multiple displacement curves crossed over one another. A two-site competitive model was required to adequately describe the interactions of these mu selective ligands with 3H-DADLE. This two-site model was one in which the inhibitor had higher affinity for the site labeled with lower affinity by 3H-DADLE. However, this two site model did not correctly predict the interaction of LE with 3H-DADLE in the presence of morphiceptin. These data indicate that: 1) putative mu and delta selective ligands do not bind to a common high affinity site; 2) mu selective ligands are not simple mixed inhibitors of a single site labeled by 3H-DADLE; and 3) competitive binding models may not explain the interaction of mu ligands with 3H-DADLE binding. 相似文献
20.
Fabricio Villalobos Francesco Carotenuto Pasquale Raia José Alexandre F. Diniz-Filho 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2016,371(1691)
Species co-occur with different sets of other species across their geographical distribution, which can be either closely or distantly related. Such co-occurrence patterns and their phylogenetic structure within individual species ranges represent what we call the species phylogenetic fields (PFs). These PFs allow investigation of the role of historical processes—speciation, extinction and dispersal—in shaping species co-occurrence patterns, in both extinct and extant species. Here, we investigate PFs of large mammalian species during the last 3 Myr, and how these correlate with trends in diversification rates. Using the fossil record, we evaluate species'' distributional and co-occurrence patterns along with their phylogenetic structure. We apply a novel Bayesian framework on fossil occurrences to estimate diversification rates through time. Our findings highlight the effect of evolutionary processes and past climatic changes on species'' distributions and co-occurrences. From the Late Pliocene to the Recent, mammal species seem to have responded in an individualistic manner to climate changes and diversification dynamics, co-occurring with different sets of species from different lineages across their geographical ranges. These findings stress the difficulty of forecasting potential effects of future climate changes on biodiversity. 相似文献