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The solid-state conformation of the first N-protected ornithine derivative has been established by X-ray analysis. The hydrochloride of N-(9-fluorenyl)methoxycarbonyl-L-ornithine crystallises as diethyl ether solvate. The backbone (0, , , 1) torsion angles are (174.9°, –84.0°, 145.9°, –171.0°). The conformation of the urethane amide bond is trans. The ornithine aliphatic side chain adopts preferred fully extended conformation which is stabilised by the hydrogen bonding of the –NH3
+ group to the diethyl ether molecule, carboxyl group and Cl- anions. 相似文献
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Beatriz G. de la Torre Miguel A. Marcos Ramon Eritja Fernando Albericio 《Letters in Peptide Science》2001,8(6):331-338
The preparation of N-trityl-amino acids is described. Several derivatives of trifunctional amino acidscarrying acid- and base-labile side-chain protecting groups and the trityl group at the N position are prepared for first time. The incorporation of N-trityl-amino acids into peptide sequences usingsolid-phase protocols was achieved. The use of the trityl groupfor the protection of the -amino group in conjunction with base-labile side-chain protecting groups constitutes a newmethod for the assembly of peptides in mild conditions. 相似文献
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A cotransport system for Na+, K+ and Cl? in Ehrlich cells is described. It is insensitive towards ouabain but specifically inhibited by furosemide and other ‘high ceiling’ diuretics at concentrations which do not affect other pathways of the ions concerned. As the furosemide-sensitive fluxes of these ions are not affected by changes in membrane potential, and as their complete inhibition by furosemide does not appreciably alter the membrane potential, they appear to be electrically silent. Application of the pulse-response methods in terms of irreversible thermodynamics reveals tight coupling between the furosemide-sensitive flows of Na+, K+ and Cl? ( close to unity for all three combinations) at a stoichiometry of 1 : 1 : 2. The site for each of the ions appears to be rather specific: K+ can be replaced by Rb+ but not by other cations tested whereas Cl? can be poorly replaced by Br? but not by NO3?, in contradistinction to the Cl?-OH? exchange system. The cotransport system appears to function in cell volume regulation as it tends to make the cell swell, thus counteracting the shrinking effect of the ouabain-sensitive (Na+, K+) pump.The experiments presented could not clarify whether the cotransport process is a primary or secondary active one; while incongruence between transport and conjugated driving force seems to indicate primary active transport, it is very unlikely that hydrolysis of ATP supplies energy for the transport process, since there is no stimulation of ATP turnover observable under operation of the cotransport system. 相似文献
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Joseph Bonaventura Celia Bonaventura Gino Amiconi Eraldo Antonini Maurizio Brunori 《Archives of biochemistry and biophysics》1974,161(1):328-332
Hemoglobin Leiden is an abnormal human hemoglobin in which a glutamic acid residue has been deleted from the β-chain at position 6 or 7. The α-amino groups of the β-chain N-termini in tetrameric hemoglobin A are thought to be directly involved in the binding of simple anions and organic phosphates (1). The deletion of the 4th or 5th residue of the A helix in hemoglobin Leiden shortens the N-terminus of the β-chain, and the results reported here show that the anion binding site has been affected. Hemoglobin Leiden shows a decreased response to inorganic phosphate, chloride, 2,3-diphosphoglycerate, and inositol hexaphosphate, both in equilibria and kinetics of ligand binding. Although hemoglobin Leiden shows an altered response to anions, neither the cooperativity of ligand binding nor the Bohr effect are significantly altered by the deletion. The decreased effect of cofactors seems to be due to a decrease in the strength of anion binding which may be attributed to the altered geometry of the anion binding site. 相似文献
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The improved methods for the preparation of valency hybrid hemoglobins, (α3+β2+)2 and (α2+β3+)2 were presented. The (α3+β2+)2 valency hybrid was separated from the solutions of partially reduced methemoglobin with ascorbic acid, by using CM 32 column chromatography. The (α2+β3+)2 valency hybrid was also isolated from hemoglobin solutions, which were partially oxidized with ferricyanide, by chromatography on CM 32 column. These valency hybrid hemoglobins were found to be single on isoelectric focusing electrophoresis. Present procedures are very simple and are suitable for the bulk preparation of (α3+β2+)2 and (α2+β3+)2 valency hybrids. 相似文献
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W.McD. Armstrong W.R. Bixenman K.F. Frey J.F. Garcia-Diaz M.G. ORegan Jeanie L. Owens 《生物化学与生物物理学报:生物膜》1979,551(1):207-219
Na+, K+ and Cl? concentrations () and activities (), and mucosal membrane potentials () were measured in epithelial cells of isolated bullfrog (Rana catesbeiana) small intestine. Segments of intestine were stripped of their external muscle layers, and bathed (at 25°C and pH 7.2) in oxygenated Ringer solutions containing 105 mM Na+ and Cl? and 5.4 mM K+. Na+ and K+ concentrations were determined by atomic absorption spectrometry and Cl? concentrations by conductometric titration following extraction of the dried tissue with 0.1 M HNO3. 14C-labelled inulin was used to determine extracellular volume. was measured with conventional open tip microelectrodes, with solid-state Cl?-selective silver microelectrodes and and with Na+- and K+-selective liquid ion-exchanger microelectrodes. The average recorded was ?34 mV. , and were 51, 105 and 52 mM. The corresponding values for , and were 18, 80 and 33 mM. These results suggest that a large fraction of the cytoplasmic Na+ is ‘bound’ or sequestered in an osmotically inactive form, that all, or virtually all the cytoplasmic K+ behaves as if in free solution, and that there is probably some binding of cytoplasmic Cl?. significantly exceeds the level corresponding to electrochemical equilibrium across the mucosal and baso-lateral cell membranes. Earlier studies showed that coupled mucosal entry of Na+ and Cl? is implicated in intracellular Cl? accumulation in this tissue. This study permitted estimation of the steady-state transapical Na+ and Cl? electrochemical potential differences (Δμ̄Na and Δμ̄Cl). Δμ̄Na (?7000 J · mol?1; cell minus mucosal medium) was energetically more than sufficient to account for Δμ̄Cl (1000–2000 J · mol?1). 相似文献
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Patrick M. Jeffries 《Inorganica chimica acta》2008,361(11):3165-3170
Treatment of the ruthenium(II) diene complexes [(η2,η2-nbd)RuCl2]n or [(η2,η2-cod)RuCl2]n with 4 equiv. of methyllithium in the presence of N,N,N′,N′-tetramethylethylenediamine (tmed) yields the methyl complexes [Li(tmed)]2[(η2,η2-nbd)RuMe4] (1) and [Li(tmed)]2[(η3,η2-C8H11)RuMe3] (2), respectively, where nbd = norbornadiene and cod = 1,5-cyclooctadiene. In the latter compound, the cyclooctadiene ligand has been deprotonated to afford a η3,η2-1,2,3:5,6-cyclooctadienyl group. Both complexes were studied by 1H and 13C{1H} NMR spectroscopy, and the crystal structure of 2 was determined. One lithium atom in 2 is four-coordinate and bridges between one ruthenium-bound methyl group and one of the wingtip allylic carbon atoms in the η3,η2-C8H11 ligand. The other lithium atom is five-coordinate, and forms contacts with the other two Ru-Me groups and with the other wingtip carbon atom of the allyl unit. 相似文献
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The balance of K+, Na+, and Cl− fluxes across the cell membrane with the Na+/K+ pump, ion channels, and Na+K+2Cl− (NKCC) and Na+-Cl− (NC) cotransport was calculated to determine the mechanism of cell shrinkage in apoptosis. It is shown that all unidirectional
K+, Na+, and Cl− fluxes; the ion channel permeability; and the membrane potential can be found using the principle of the flux balance if
the following experimental data are known: K+, Na+, and Cl− concentrations in cell water; total Cl− flux; total K+ influx; and the ouabain-inhibited pump component of the Rb+(K+) influx. The change in different ionic pathways during apoptosis was estimated by calculations based on the data reported
in the preceded paper (Yurinskaya et al., 2010). It is found that cell shrinkage and the shift in ion balance in U937 cells
induced to apoptosis with 1 μM staurosporine occur due to the coupling of reduced pump activity with a decrease in the integral
permeability of Na+ channels, whereas K+ and Cl− channel permeability remains almost unchanged. Calculations show that only a small part of the total fluxes of K+, Na+, and Cl− account for the fluxes mediated by NKCC and NC cotransporters. Despite the importance of cotransport fluxes for maintaining
the nonequilibrium steady-state distribution of Cl−, they cannot play a significant role in apoptotic cell shrinkage because of their minority and cannot be revealed by inhibitors. 相似文献
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The heme iron of the β chains of mammalian hemoglobins are rapidly and selectively oxidized in the presence of excess Cu(II) ions in a reaction that requires the presence of a free -SH groups on the β globin chain. The presence of freely reactive -SH groups on the α chains of cat and sheep hemoglobins does not alter the course of this reaction: only the β hemes are oxidized rapidly by Cu(II) in these hemoglobins. Two equivalents of copper are required for the rapid oxidation of the two β chain hemes per mole of cat hemoglobin, in contrast with the four equivalents that are required for reaction with human hemoglobin. The human-cat hybrid hemoglobins, α2Humanβ2Cat and α2Catβ2Human, required two and four equivalents of copper/mol, respectively, for the reaction. Thus, the kinetics and stoichimetry of the reaction are determined by the nature of the β subunit. Analysis of the esr spectra of the products of the reaction of Cu(II) with these hemoglobins indicate that human hemoglobin and the hybrid α2Catβ2Human contain tight binding sites for two equivalents of Cu(II) that are not involved in the oxidation reaction and are not present in cat hemoglobin or α2Humanβ2Cat. Cat β globin like others (sheep, bovine) that lack the tight binding site, has no histidine residue at 2β. It has phenylalanine in this position. These results support the suggestion of Rifkind et al. (Biochemistry 15,5337[1976]) that the tight binding site is near the amino terminal region of the β chain and is associated with histidine 2β. 相似文献
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Haruhisa Mita Hiroshi Yasueda Takao Shida 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1980,221(1):1-7
A new and sensitive method is described for the determination of histamine and Nτ-methylhistamine in human plasma and urine by gas chromatography-mass spectrometry. 15N2-Labeled histamine and Nτ-[methyl-d3]methylhistamine were used as internal standards. Histamine and Nτ-methylhistamine were converted to the derivatives Nα-heptafluorobutyryl-Nτ-ethoxycarbonylhistamine and Nα-heptafluorobutyryl-Nτ-methylhistamine, respectively. After these derivatives had been purified on a small column packed with CPG-10, the molecular ions were monitored during selected ion monitoring. Linear standard curves were obtained in the range of 0.5–10 ng/ml for both compounds. The reliability of the histamine analysis was demonstrated by using two different ion pairs, while a comparison with results from two different derivatizations on the same urine sample also established the specificity of the Nτ-methylhistamine analysis. An increase of 1 ng of histamine in the plasma could be precisely determined by the present method. The histamine content of plasma from five normal subjects was determined as 0.83 ÷ 0.37 (S.D.) ng/ml and the Nτ-methylhistamine content in most subjects was below the limits of this measurement. High excretion of histamine was noted in the urine collected in the early morning from a patient with nephritis. 相似文献
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Ca2+-dependent inhibitory effects of Na+ and K− on Ca2+ transport in sarcoplasmic reticulum vesicles
Effects of Na+ and K+ on Ca2+ transport by sarcoplasmic reticulum vesicles were studied in a medium containing high Mg2+ and ATP (2mM) and low Ca2+ (0.44μM) concentrations. Under these conditions, Na+ and K+ inhibit Ca2+ uptake. ATPase activity and membrane phosphorylation by ATP. Since the concentrations of ATP and Ca2+ used are consistent with relaxation in vivo, the results suggest that under physiological resting conditions the Ca2+ pump of the sarcoplasmic reticulum operates below its maximal capacity. 相似文献
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Mitsuhide Noshiro Shin-ichi Hayashi Kuniko Murakami Kyuichiro Okuda 《Biochemical and biophysical research communications》1982,106(3):927-932
Role of cytochrome b5 in NADPH-supported 5β-cholestane-3α,7α,12α-triol 25-hydroxylation and taurodeoxycholate 7α-hydroxylation of rat liver microsomes was investigated using highly purified antibodies against cytochrome b5. Anti-b5 antibody strongly inhibited both hydroxylation reactions indicating that cytochrome b5 is a functional component in these steroid hydroxylation systems. It was shown that the involvement of cytochrome b5 in these systems could be altered by the conditions of the reaction systems. 相似文献
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The effect of changing [K+], [Na+] and [Cl?] in nutrient solution was studied in bullfrog antrum with and without HCO3? in nutrient. In 25 mM HCO3? (95% O2/5% CO2) and in zero HCO3? (100% O2), nutrient pH was maintained at 7.3. Changing from 4 to 40 mM K+ or from 81 to 8.1 mM Cl? gave a decrease 10 min later in transmucosal PD (nutrient became more negative) — a normal response. These responses were less in zero than in 25 mM HCO3?. A decrease from 102 to 8 mM Na+ decreased PD (anomalous response of electrogenic NaCl symport). This effect was attenuated or eliminated in zero HCO3?. In contrast, change from 4 to 40 mM K+ gave initial anomalous PD response and change from 102 to 8 mM Na+, initial normal PD response with either zero or 25 mM HCO3?. Both responses were associated with (Na+ + K+)-ATPase pump and were greater in zero than in 25 mM HCO3?. Initial PD increases in zero HCO3? are explained as due to increase in the resistance of passive conductance and/or NaCl symport pathways. Thus, removal of HCO3? modifies conductance pathways of nutrient membrane. 相似文献
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Satoshi Hamada Yoshiko Moriyama Koji Yamaguchi Kunio Takeda 《Journal of Protein Chemistry》1994,13(4):423-428
The peptide bond between Asp66-Pro67 of -lactalbumin was cleaved with formic acid (cleaved-lactalbumin). Secondary structural changes of the cleaved-lactalbumin, in which the two separated polypeptides were joined by disulfide bridges, were examined in solutions of sodium dodecyl sulfate (SDS), urea, and guanidine hydrochloride. The structural changes of the cleaved-lactalbumin were compared with those of the intact protein. The relative proportions of secondary structures were determined by curve fitting of the circular dichroism spectrum. The cleaved-lactalbumin contained 29%-helical structure as against 34% for the intact protein. Some helices of the cleaved-lactalbumin which had been disrupted by the cleavage appeared to be reformed upon the addition of SDS of very low concentration (0.5mM). In the SDS solution, the helicities of both the intact and cleaved proteins increased, attaining 44% at 4mM SDS. On the other hand, the helical structures of the cleaved-lactalbumin began to be disrupted at low concentrations of guanidine hydrochloride and urea compared with that of the intact protein. However, no diffrence was observed in the thermal denaturations of the intact and cleaved proteins, except for the difference in the original helicities. The helicities of both proteins decreased with an increase of temperature up to 65°C and recovered upon cooling. 相似文献
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(Na+/K+)-ATPase研究概况 总被引:7,自引:0,他引:7
谢静平 《生物化学与生物物理进展》1989,16(4):256-260
本文概述(Na+/K+)-ATPase的一般分子性质。介绍神经元和脂肪细胞中两种不同分子形式(Na+/K+)-ATPase的分离鉴定和功能性质,以及(Na+/K+)-ATPase主要功能亚基一级序列和高级结构研究所取得的一些进展。 相似文献