共查询到20条相似文献,搜索用时 31 毫秒
1.
R Kr?mer 《Biochimica et biophysica acta》1980,592(3):615-620
1. Divalent cations cause a decrease in the exchange activity of the reconstituted ADP,ATP translocator from beef heart mitochondria. This effect is due to complex formation with the adenine nucleotides. 2. It is confirmed that only the free nucleotides are transported. A possible competition of free adenine nucleotides and the Mg2+-complexes for the binding site at the carrier protein is excluded. 3. The stability constants (Kn) for the cation-nucleotide complexes are derived from these experiments. For Mg2+-ATP, Kn = 0.8 x 10(4) M-1 and for Mg2+-ADP, Kn = 0.8 x 10(3) M-1 is obtained. 4. The carrier system was reconstituted with the neutral phospholipids phosphatidylcholine and phosphatidylethanolamine. Interaction of the divalent cations with these phospholipids seem not to be important for the exchange suppression. 相似文献
2.
Qualitative estimates of the relative stability of hypothetical heterofullerenes C55Y5 (Y=Si, Ge, Sn, B, Al, N, P, SiH, GeH, SnH) and some η5-π-complexes LiC55Y5 were carried out by the MNDO method. Atoms Y (or groups XH) are assumed to substitute those C atoms in fullerene C60 which are located at the -positions of a separated pentagonal face (pent*) of this polyhedral molecule. It is shown that the spin densities in radicals C55Y5 (Y=SiH, GeH, SnH, B, Al, N, P) are localized on the separated pentagon atoms and the Li-pentagonal face (Li-pent*) bonds in η5-π-complexes of these radicals with the Li atom are considerably stronger than Li-pent* bonds in complexes [η5-π-LiC60]+ and [η5-π-LiC60] of unsubstituted C60. In addition, it is established that the Li-pent* bond energies in η5-π-complexes LiC55B5 and LiC55Al5 exceed the energy of the Li-pent* bond in the η5-π-complex LiC60H5 studied earlier. In contrast, the energies of similar bonds for Y=N, P are close to the energy of the Li-pent* bond in the η5-π-complex LiC60H5. 相似文献
3.
Mixtures of anionic HgCl3-/HgCl4(2)-complexes were less toxic to terrestrial bacteria (Erwinia herbicola, Agrobacterium tumefaciens), to marine bacteria (Acinetobacter sp., Aeromonas sp.), and to bacteriophages (phi 11 M 15 of Staphylococcus aureus and P1 of Escherichia coli) than were equivalent concentrations of Hg as cationic Hg2+. The toxicity of 1 ppm Hg to A. tumefaciens. Aeromonas sp., and phi 11 M 15 was less in seawater than in lake water. Inasmuch as the Hg-Cl species are formed in environments of high chloride concentration, it was postulated that the lower toxicity of Hg in seawater was a result of the formation of HgCl3-/HgCl4(2)-complexes. 相似文献
4.
The major goal of this review is a critical discussion of the literature data on asymmetric synthesis of α-amino acids via Michael addition reactions involving Ni(II)-complexes of amino acids. The material covered is divided into two conceptually different groups dealing with applications of: (a) Ni(II)-complexes of glycine as C-nucleophiles and (b) Ni(II)-complexes of dehydroalanine as Michael acceptors. The first group is significantly larger and consequently subdivided into four chapters based on the source of stereocontrolling element. Thus, a chiral auxiliary can be used as a part of nucleophilic glycine Ni(II) complex, Michael acceptor or both, leading to the conditions of matching vs. mismatching stereochemical preferences. The particular focus of the review is made on the practical aspects of the methodology under discussion and mechanistic considerations. 相似文献
5.
Interactions of Streptomyces subtilisin inhibitor with Streptomyces griseus proteases A and B. Enzyme kinetic and computer simulation studies 总被引:1,自引:0,他引:1
U Christensen S Ishida S Ishii Y Mitsui Y Iitaka J McClarin R Langridge 《Journal of biochemistry》1985,98(5):1263-1274
Streptomyces subtilisin inhibitor (SSI), a dimeric protein that strongly inhibits subtilisins, was shown to form tight inhibitory complexes with Streptomyces griseus proteases A and B (SGPA and SGPB). The apparent dissociation constants of the SGPA-SSI and SGPB-SSI complexes were found to be orders of magnitude less than those of subtilisin-SSI complexes. Using the known atomic coordinates for SGPA and SSI, the highly complementary nature of the surface geometries of the two proteins was confirmed by a computer graphics study, which led to a proposed structure for the SGPA-SSI complex. Kinetic studies further suggested that the SSI dimer can bind two molecules of either SGPA or SGPB, and the 2:1-complexes (consisting of one inhibitor dimer and one enzyme molecule) apparently possess lower intrinsic dissociation constants than the 2:2-complexes. It was also shown that both of SGPA and SGPB are inhibited by both soybean trypsin inhibitor (Kunitz) and bovine pancreatic trypsin inhibitor (Kunitz), but far less strongly than by SSI. 相似文献
6.
Carrasco-Pozo C Aliaga ME Olea-Azar C Speisky H 《Bioorganic & medicinal chemistry》2008,16(22):9795-9803
The present study investigated the redox-consequences of the interaction between various endogenous thiols (RSH)-glutathione, cysteine, homocysteine, gamma-glutamyl-cysteine, and cysteinyl-glycine- and Cu(2+) ions, in terms of their free radical-scavenging, ascorbate-oxidizing and O2(*-)-generating properties of the resulting mixtures. Upon a brief incubation (3-30 min) with Cu(2+), the free radical-scavenging properties (towards ABTS(*)(+) and DPPH(*)) and thiol-titratable groups of the RSH added to the mixtures decreased significantly. Remarkably, both effects were only partial, even in the presence of a large molar Cu(2+)-excess, and were unaffected despite increasing the incubation time. At equimolar concentrations, the RSH/Cu(2+) mixtures led to the formation of (EPR paramagnetic) Cu(II)-complexes that were time-stable and ascorbate-reducible, but redox-inactive towards oxygen. In turn, at a slight molar thiol-excess (3:1), the mixtures resulted in the formation of time-stable Cu(I)-complexes (EPR silent) that were unreactive towards ascorbate and oxygen. The only exception was seen for the thiol, glutathione, whose mixture with Cu(2+) mixture displayed a O2(*-)-generating capacity (cytochrome c- and lucigenin-reduction). The data indicate that, depending on their molar ratio, the interaction between Cu(2+) and the tested thiols would give place to mixtures containing either: (i) time-stable and ascorbate-reducible Cu(II)-complexes which display free radical-scavenging properties, or (ii) time-stable but redox-inactive towards oxygen Cu(I)-complexes. Among the latter, the only exception was that of glutathione. 相似文献
7.
INGEGERD FÄNGSTRÖM 《Physiologia plantarum》1972,27(3):389-397
The effects on apparent photosynthesis in the green alga Scenedesmus quadricauda of four chelating substances, 8-hydroxyquinoline (= oxine), β-isopropyltropolone (=β-thujaplicin), sodium dimethyldithiocarbamate and 3-(β-hydroxyethyl)-C-pentamethylene-3-aza-dithiocarbamate have been investigated. The first three compounds mentioned had all an inhibitory effect on photosynthesis, measured as oxygen production with a manometric, a volumetric or a polarographic method. In combination with certain concentrations of CuSO4 bimodal dose response curves were observed, similar to those obtained on the growth of different microorganisms. Calculations of the amounts of different complexes that appeared in the nutrient solutions during the experiments are compared with the recorded degrees of inhibition. The results strongly indicate that the 1: 1-complexes between Cu2+ and the chelating substances are the most toxic agents at low concentrations of these compounds. 相似文献
8.
WNK (with no lysine (K)) protein kinases are found in many eukaryotes and share a unique active site. Here, we report that a member of the Arabidopsis WNK family (AtWNK8) interacts with subunit C of the vacuolar H+-ATPase (V-ATPase) via a short C-terminal domain. AtWNK8 is shown to autophosphorylate intermolecularly and to phosphorylate Arabidopsis subunit C (AtVHA-C) at multiple sites as determined by MALDI-TOF MS analysis. Furthermore, we show that AtVHA-C and other V-ATPase subunits are phosphorylated when V1-complexes are used as substrates for AtWNK8. Taken together, our results provide evidence that V-ATPases are potential targets of WNK kinases and their associated signaling pathways. 相似文献
9.
Christer B. Aakeröy John Desper Jesús Valdés-Martínez 《Inorganica chimica acta》2006,359(4):1255-1262
We have prepared two ligands, 4- and 5-carboxylic acid pyrimidine, and synthesized and crystallographically characterized seven coordination complexes thereof. The need for potentially structurally disruptive counterions is eliminated by deprotonation of the carboxylic acid moieties; the carboxylates present in each structure act as counterions and balance the charge on the divalent metal ions leading to charge-neutral complex ions. The four new M(II)-complexes with 4-carboxylic acid pyrimidine (M = Ni, Cu, Zn, and Co) are isostructural as are the three M(II) complexes with 3-carboxylic acid pyrimidine (M = Ni, Cu, and Zn), indicating robust and reliable coordination modes for both ligands. 相似文献
10.
Lokesh Bhattacharyya C.Fred Brewer Rodney D. Brown Seymour H. Koenig 《Biochemical and biophysical research communications》1984,124(3):857-862
Ca2+-Zn2+-derivatives of lentil and pea lectins were prepared for the first time by a unique method involving dialysis of the native Ca2+-Mn2+-lectins against large excesses of metal ions in pH 4.0 buffer. Each derivative contained about 1.5 g atoms of Ca2+ and about 1 g atom of Zn2+ per monomer. The derivatives were found to be identical to their respective native forms, both in molecular weight and carbohydrate binding activities. Solvent proton relaxation dispersion measurements were used to characterize both the Ca2+-Zn2+- and Ca2+-Mn2+-complexes of the lentil lectin. 相似文献
11.
A considerable limitation of NMR spectroscopy is its inherent low sensitivity. Approximately 90 % of the measuring time is used by the spin system to return to its Boltzmann equilibrium after excitation, which is determined by 1H-T1 in cross-polarized solid-state NMR experiments. It has been shown that sample doping by paramagnetic relaxation agents such as Cu2+-EDTA accelerates this process considerably resulting in enhanced sensitivity. Here, we extend this concept to Gd3+-complexes. Their effect on 1H-T1 has been assessed on the membrane protein proteorhodopsin, a 7TM light-driven proton pump. A comparison between Gd3+-DOTA, Gd3+-TTAHA, covalently attached Cu2+-EDTA-tags and Cu2+-EDTA reveals a 3.2-, 2.6-, 2.4- and 2-fold improved signal-to-noise ratio per unit time due to longitudinal paramagnetic relaxation enhancement. Furthermore, Gd3+-DOTA shows a remarkably high relaxivity, which is 77-times higher than that of Cu2+-EDTA. Therefore, an order of magnitude lower dopant concentration can be used. In addition, no line-broadening effects or peak shifts have been observed on proteorhodopsin in the presence of Gd3+-DOTA. These favourable properties make it very useful for solid-state NMR experiments on membrane proteins. 相似文献
12.
D Mustafi Y Nakagawa M W Makinen 《Cellular and molecular biology, including cyto-enzymology》2000,46(8):1345-1360
Nephrocalcin inhibits the growth of calcium oxalate monohydrate crystals in the mammalian kidney. Isoforms A and B contain three equivalents of gamma-carboxyglutamic acid (Gla) residues implicated in Ca2+-binding and exhibit strong inhibitor properties and high Ca2+-binding affinity (Kd approximately 10(-8) M). Isoforms C and D lack these properties and exhibit low Ca2+-binding affinity (Kd approximately 10(-6) M). With VO2+ as a structural probe, electron paramagnetic resonance (EPR) studies of the Ca2+-binding sites of isoforms B and D showed that VO2+ binds competitively with a metal ion:protein stoichiometry of 4:1. EPR spectral parameters of the VO2+ ion were consistent with only equatorial oxygen-donor ligands. EPR and angle-selected electron nuclear double resonance (ENDOR) spectra showed two equatorially positioned, metal coordinating waters in isoform D while in isoform B no ligands undergoing hydrogen exchange were found. Since isoform D showed no evidence for axially coordinated water, similarly to isoform B, it is likely that the protein residues occupying the axial sites are identical in both proteins. ENDOR spectra of VO2+-complexes of isoforms B and D were compared to spectra of the VO2+-complex with alpha-ethylmalonic acid (EMA), a molecular mimic of Gla. Spectra of the VO2+-complex of EMA showed axial water located trans to the V=O bond and outer shell water hydrogen-bonded to the vanadyl oxygen, consistent with the X-ray structure of Ca(EMA)2. We, therefore, conclude that the spatial disposition of carboxylate groups of Gla residues coordinating Ca2+ in isoforms A and B must differ from that observed in the crystal structure of Ca(EMA)2. 相似文献
13.
14.
The enantioselective alkynylation of aldehyde catalyzed by chiral zinc(II)-complexes was studied by means of the density functional
theory (DFT). All the structures were optimized completely at the B3LYP/6-31G(d,p) level. To obtain more exact energies, single-point
energy calculations at B3LYP/6-31+G(d,p) level were carried out on the B3LYP/6-31G(d,p) geometries. As shown, this enantioselective
alkynylation was endothermic. The chirality-determining step for the alkynylation was the formation of the catalyst–ethanol
complexes and the transition states for this step involved a six-membered ring. The dominant products predicted theoretically
were of (R)-chirality, in good agreement with experiment.
相似文献
15.
Ascorbate and complexes of Cu(II) and Fe(III) are capable of generating significant levels of oxygen free radicals. Exposure
of erythrocytes to such oxidative stress leads to increased levels of methemoglobin and extensive changes in cell morphology.
Cu(II) per mole is much more effective than Fe(III). However, isolated hemoglobin is oxidized more rapidly and completely
by Fe(III)- than by Cu(II)-complexes. Both Fe(III) and Cu(II) are capable of inhibiting a number of the key enzymes of erythrocyte
metabolism. The mechanism for the enhanced activity of Cu(II) has not been previously established. Using intact erythrocytes
and hemolysates we demonstrate that Cu(II)-, but not Fe(III)-complexes in the presence of ascorbate block NADH-methemoglobin
reductase. Complexes of Cu(II) alone are not inhibitory. The relative inability of Fe(III)-complexes and ascorbate to cause
methemoglobin accumulation is not owing to Fe(III) association with the membrane, or its failure to enter the erythrocytes.
The toxicity of Cu(II) and ascorbate appears to be a result of site-specific oxidative damage of erythrocyte NADH-methemoglobin
reductase and the enzyme's subsequent inability to reduce the oxidized hemoglobin. 相似文献
16.
An F0F1-ATPase was isolated from the membranes of the marine bacterium Vibrio alginolyticus. Homology between the subunits of the F0-complexes from E. coli and V. alginolyticus was found using antibodies against subunits a, b and c of the E. coli F0F1-ATPase. The F0F1-complex from V. alginolyticus was reconstituted into proteoliposomes, which were competent in ATP-dependent proton uptake. This process was inhibited by triphenyltin, DCCD, and venturicidin. Na+ did not affect proton translocation. 相似文献
17.
18.
During cotranslational translocation of proteins into the endoplasmic reticulum (ER) translating ribosomes bind to Sec61-complexes. Presently two models exist how these membrane protein complexes might form protein-conducting channels. While electron microscopic data suggest that a ring-like structure consisting of four Sec61-complexes build the channel, the recently solved crystal structure of a homologous bacterial protein complex led to the speculation that the actual tunnel is formed by just one individual Sec61-complex. Using protease protection assays together with quantitative immunoblotting we directly examined the structure of mammalian protein-conducting channels. We found that in native ER-membranes one single Sec61alpha-molecule is preferentially protected by a membrane bound ribosome, both, in the presence and absence of nascent polypeptides. In addition we present evidence that the nascent polypeptide destabilizes the ring-like translocation apparatus formed by four Sec61-complexes. Moreover, we found that after solubilization of ER-membranes a single Sec61-complex is sufficient to protect the nascent polypeptide chain against added proteases. Finally, we could show that this single Sec61-complex allows the movement of the nascent chain, when it has been released from the ribosome by puromycin treatment. Collectively, our data suggest that the active protein-conducting channel in the ER is formed by a single Sec61-complex. 相似文献
19.
Sissi C Mancin F Palumbo M Scrimin P Tecilla P Tonellato U 《Nucleosides, nucleotides & nucleic acids》2000,19(8):1265-1271
The hydrolytic activity of the 1,3,5-triaminocyclohexane derivatives TACH, TACI and TMCA complexed to Zn(II) and Cu(II) towards a model phosphoric ester and plasmid DNA has been evaluated by means of spectroscopic and gel-electrophoresis techniques. At conditions close to physiological, a prominent cleavage effect mediated by the nature of the ligand and metal ion was generally observed. TACI complexes are the most active in relaxing supercoiled DNA, the effect being explained by the affinity of the hydroxylated ligand for the nucleic acid. As indicated by the dependence of cleavage efficiency upon pH, Zn(II)-complexes act by a purely hydrolytic mechanism. In the case of Cu(II)-complexes, although hydrolysis should be prominent, involvement of an oxidative pathway cannot be completely ruled out. 相似文献
20.
The hydrolysis of two neutral phosphate esters, (tris-2-pyridylphosphate and tris-p-nitrophenylphosphate, 5 and 4 respectively) and a phosphonate ester (ethyl-p-nitrophenylmethylphosphonate (6)) were studied in the presence of Co2+-complexes of two tris- imidazolylphosphines. In the hydrolyses of both 5 and 6, the Co2+-complex of bis-[4,5-diisopropyl- imidazol-2-yl]imidazole-2-yl phosphine (2) appears to act as the anionic form, generated by ionization of a Co2+-bound H2O having a pKa of ~8 at 37 °C in 80% ethanol-H2O. On the other hand, the Co2+-complex of bis-[4,5-diisopropylimidazol-2-yl]-4(5)- hydroxyethylimidazol-2-yl phosphine (3) catalyses the hydrolyses of 5 and 6 with an activity which increases linearly with pH. In this case, the active form of Co2+:3 has a pKa in excess of 8.3 which apparently obtains from ionization of the Co2+- associated hydroxyethyl group. Evidence is presented that Co2+:3 functions as a general base catalyst in the hydrolysis of 5. 相似文献