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Active Complex (active + complex)
Selected AbstractsCytosolic chaperonin-containing t-complex polypeptide 1 changes the content of a particular subunit species concomitant with substrate binding and folding activities during the cell cycleFEBS JOURNAL, Issue 17 2001Shin-ichi Yokota The chaperonin-containing t-complex polypeptide 1 (CCT) is a cytosolic molecular chaperone composed of eight subunits that assists in the folding of actin, tubulin and other cytosolic proteins. We show here that the content of particular subunits of CCT within mammalian cells decreases concomitantly with the reduction of chaperone activity during cell cycle arrest at M phase. CCT recovers chaperone activity upon resumption of these subunits after release from M phase arrest or during arrest at S phase. The levels of ,, , and ,-1 subunits decreased more rapidly than the other subunits during M phase arrest by colcemid treatment and recovered after release from the arrest. Gel filtration chromatography or native (nondenaturing) PAGE analysis followed by immunoblotting indicated that the , and , subunit content in the 700- to 900-kDa CCT complex was appreciably lower in the M phase cells than in asynchronous cells. In vivo, the CCT complex of M-phase-arrested cells was found to bind lower amounts of tubulin than that of asynchronous cells. In vitro, the CCT complex of M phase-arrested cells was less active in binding and folding denatured actin than that of asynchronous cells. On the other hand, the CCT complex of asynchronous cells (a mixture of various phases of cell cycle) exhibited lower , and , subunit content and lower chaperone activity than that of S-phase-arrested cells obtained by excess thymidine treatment. In addition, turnover (synthesis and degradation) rates of the , and , subunits in vivo were more rapid than those of most other subunits. These results suggest that the content of , and , subunits of CCT reduces from the complete active complex in S phase cells to incomplete inactive complex in M phase cells. [source] Zymogen activation in the streptokinase,plasminogen complexFEBS JOURNAL, Issue 13 2000Ile1 is required for the formation of a functional active site Plasminogen (Plgn) is usually activated by proteolysis of the Arg561,Val562 bond. The amino group of Val562 forms a salt-bridge with Asp740, which triggers a conformational change producing the active protease plasmin (Pm). In contrast, streptokinase (SK) binds to Plgn to produce an initial inactive complex (SK·Plgn) which subsequently rearranges to an active complex (SK·Plgn*) although the Arg561,Val562 bond remains intact. Therefore another residue must substitute for the amino group of Val562 and provide a counterion for Asp740 in this active complex. Two candidates for this counterion have been suggested: Ile1 of streptokinase and Lys698 of Plgn. We have investigated the reaction of SK mutants and variants of the protease domain of microplasminogen (µPlgn) in order to determine if either of these residues is the counterion. The mutation of Ile1 of SK decreases the activity of SK·Plgn* by 100-fold (Ile1Val) to ,,104 -fold (Ile1,Ala, Gly, Trp or Lys). None of these mutations perturb the binding affinity of SK, which suggests that Ile1 is not required for formation of SK·Plgn but is necessary for SK·Plgn*. The substitution of Lys698 of µPlgn decreases the activity of SK·Plgn* by only 10,60-fold. In contrast with the Ile1 substitutions, the Lys698 mutations also decreased the dissociation constant of the SK complex by 15,50-fold. These observations suggest that Lys698 is involved in formation of the initial SK·Plgn complex. These results support the hypothesis that Ile1 provides the counterion for Asp740. [source] Thiosemicarbazone Salicylaldiminato-Palladium(II)-Catalyzed Mizoroki,Heck ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Guanlei Xie Abstract Four tridentate thiosemicarbazone salicylaldiminato-palladium(II) complexes of the general formula [Pd(saltsc-R)PPh3] [saltsc=salicylaldehyde thiosemicarbazone; R=H (1), 3- tert -butyl (2), 3-methoxy (3), 5-chloro (4)], have been evaluated as catalyst precursors for the Mizoroki,Heck coupling reaction between a variety of electron-rich and electron-poor aryl halides and olefins. The palladium complexes (0.1,1,mol% loading) were found to effectively catalyze these reactions with high yields being obtained when aryl iodides and aryl bromides were utilized. The effects of base, catalyst loading, reaction temperature and reaction time on the catalytic activity of the most active complex were also investigated. [source] Src is a major signaling component for CTGF induction by TGF-,1 in osteoblasts,JOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2010X. Zhang Connective tissue growth factor (CTGF/CCN2) is induced by transforming growth factor ,1 (TGF-,1) where it acts as a downstream mediator of TGF-,1 induced matrix production in osteoblasts. We have shown the requirement of Src, Erk, and Smad signaling for CTGF induction by TGF-,1 in osteoblasts; however, the potential interaction among these signaling pathways remains undetermined. In this study we demonstrate that TGF-,1 activates Src kinase in ROS17/2.8 cells and that treatment with the Src family kinase inhibitor PP2 prevents Src activation and CTGF induction by TGF-,1. Additionally, inhibiting Src activation prevented Erk activation, Smads 2 and 3 activation and nuclear translocation by TGF-,1, demonstrating that Src is an essential upstream signaling partner of both Erk and Smads in osteoblasts. MAPKs such as Erk can modulate the Smad pathway directly by mediating the phosphorylation of Smads or indirectly through activation/inactivation of required nuclear co-activators that mediate Smad DNA binding. When we treated cells with the Erk inhibitor, PD98059, it inhibited TGF-,1-induced CTGF protein expression but had no effect on Src activation, Smad activation or Smad nuclear translocation. However PD98059 impaired transcriptional complex formation on the Smad binding element (SBE) of the CTGF promoter, demonstrating that Erk activation was required for SBE transactivation. These data demonstrate that Src is an essential upstream signaling transducer of Erk and Smad signaling with respect to TGF-,1 in osteoblasts and that Smads and Erk function independently but are both essential for forming a transcriptionally active complex on the CTGF promoter in osteoblasts. J. Cell. Physiol. 224: 691,701, 2010. © 2010 Wiley-Liss, Inc. [source] In situ polymerization of polyethylene/clay nanocomposites using a novel clay-supported Ziegler-Natta catalystPOLYMER COMPOSITES, Issue 10 2009Ahmad Ramazani S.A. Polyethylene/clay nanocomposites (PECNC) were synthesized via in situ Ziegler-Natta catalyst polymerization. Activated catalyst for polymerization of ethylene monomer has been prepared at first by supporting of the cocatalyst on the montmorillonite (MMT) smectite type clay and then active complex for polymerization formed by reaction of TiCl4 and aluminum oxide compound on the clay. Acid wash treatment has been used for increasing hydroxyl group and porosity of the clay and subsequently activity of the catalyst. The nanostructure of composites was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Obtained results show that silica layers of the mineral clay in these polyethylene/nanocomposites were exfoliated, intercalated, and uniformly dispersed in the polyethylene matrix even at very high concentration of the clay. Thermogravimetric analysis (TGA) shows good thermal stability of the PECNCs. Differential scanning calorimeter (DSC) results reveal considerable decrease in the crystalline phase of the PECNC samples. Results of permeability analysis show an increase in barrier properties of PECNC films. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers [source] Electrochemical study on interaction of vincristine with tubulinCHINESE JOURNAL OF CHEMISTRY, Issue 11 2001Yong Yu Abstract In Tris (0.005 mol/L)-NaCl (0.05 mol/L) buffer solution (pH = 7.10), keeping temperature at 37°C, a highly sensitive reduction peak of the antitumor agent was obtained by linear sweep voltammetry. The peak potential is-1.56 V (vs. SCE). The peak current is proportional to the concentration of vincristine over the range of 2.1 ± 10,7 -4.2 ± 10,6 mol/L with the detection limit of 1.0 ± 10,7 mol/L. The behavior of the binding of vincristine to tubulin was studied. The results showed that the reaction of tubulin dimer with vincristine formed an electrochemically active complex to be 1:2. Its stability constant is 2.5 ± 1014. The reduction process of the complex is irreversible with adsorptive characteristics. [source] Cobalt(III) Complexes of a Tripodal Ligand Containing Three Imidazole Groups: Properties and Structures of Racemic and Optically Active SpeciesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2008Hirofumi Nakamura Abstract The complex [Co(H3L)](ClO4)3·H2O (1), where H3L {tris[2-(4-imidazoylmethylideneamino)ethyl]amine} is a tripodal ligand obtained by condensation of tris(2-aminoethyl)amine and 4-formylimidazole in a 1:3 molar ratio, was synthesized and optically resolved by fractional crystallization of the diastereomeric salt with [Sb2{(R,R)-tart}2]2, [(R,R)-tart = (2R,3R)-tartrate(4,) ion]. From the less soluble part, ,-[Co(H2L)][Sb2{(R,R)-tart}2]·4H2O (2) was isolated. Starting from 2, two optically active complexes, ,-[Co(H3L)](ClO4)3·1.5H2O (,- 1) and ,-[Co(L)] (,- 3), were obtained. The crystal structures of these complexes are compared with those of the racemic structures. ,- 1 shows an unusually strong circular dichroism (, = 488 nm, ,, = ,7.74 M,1,cm,1) in the first d,d absorption band region. The effects of deprotonation,reprotonation of the uncoordinated imidazole NH groups of ,-[Co(H3L)]3+ on the UV/Vis and CD spectra and on the cyclic voltammograms were studied in methanol. Although the deprotonation,reprotonation reactions are reversible, the redox couple for the completely deprotonated species [CoIII/II(L)]0/, is not observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Re-oxygenation of hypoxic simian virus 40 (SV40)-infected CV1 cells causes distinct changes of SV40 minichromosome-associated replication proteinsFEBS JOURNAL, Issue 9 2002Hans-Jörg Riedinger Hypoxia interrupts the initiation of simian virus 40 (SV40) replication in vivo at a stage situated before unwinding of the,origin region. After re-oxygenation, unwinding followed by a synchronous round of viral replication takes place. To,further characterize the hypoxia-induced inhibition of unwinding, we analysed the binding of several replication proteins to the viral minichromosome before and after re-oxygenation. T antigen, the 34-kDa subunit of replication protein A (RPA), topoisomerase I, the 48-kDa subunit of primase, the 125-kDa subunit of polymerase ,, and the 37-kDa subunit of replication factor C (RFC) were present at the viral chromatin already under hypoxia. The 70-kDa subunit of RPA, the 180-kDa subunit of polymerase ,, and proliferating cell nuclear antigen (PCNA) were barely detectable at the SV40 chromatin under hypoxia and significantly increased after re-oxygenation. Immunoprecipitation of minichromosomes with T antigen-specific antibody and subsequent digestion with micrococcus nuclease revealed that most of the minichromosome-bound T antigen was associated with the viral origin in hypoxic and in re-oxygenated cells. T antigen-catalysed unwinding of the SV40 origin occurred, however, only after re-oxygenation as indicated by (a) increased sensitivity of re-oxygenated minichromosomes against digestion with single-stranded DNA-specific nuclease P1; (b) stabilization of RPA-34 binding at the SV40 minichromosome; and (c) additional phosphorylations of RPA-34 after re-oxygenation, probably catalysed by DNA-dependent protein kinase. The results presented suggest that the subunits of the proteins necessary for unwinding, primer synthesis and primer elongation first assemble at the SV40 origin in form of stable, active complexes directly before they start to work. [source] Effects of the Reaction Conditions on the Syndiospecific Polymerization of Propene Promoted by Bis(phenoxyimine) Titanium CatalystsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 4 2004Marina Lamberti Abstract Summary: The propene polymerization behavior of two typical bis(phenoxyimine) titanium catalysts has been investigated by varying reaction conditions, such as the monomer concentration, the solvent, and the cocatalyst. The experimental results indicate that the stereoregularity and regioregularity of the obtained poly(propylene)s are significantly affected by the reaction conditions. Fractionation of some poly(propylene) samples indicates the formation of macromolecules of different stereoregularity in the same run, suggesting that different active complexes can be generated in situ from these bis(phenoxyimine) titanium precatalysts. [source] Reversal of immune thrombocytopenia in mice by cross-linking human immunoglobulin G with a high-affinity monoclonal antibodyBRITISH JOURNAL OF HAEMATOLOGY, Issue 1 2006Renée Bazin Summary Intravenous immunoglobulins (IVIgs) are used to treat an increasing number of autoimmune diseases, but their exact mechanism of action remains unknown. This study showed that cross-linking of human IgG present in IVIg preparations using a mouse monoclonal anti-human IgG generated complexes that prevented or reversed thrombocytopenia in mice more efficiently than IVIg. Furthermore, biologically active complexes were obtained simply by adding the monoclonal antibody to human serum. These results suggest the possible development of an IVIg-free substitute through the ex vivo, and possibly in vivo, formation of immune complexes containing autologous IgG of immune thrombocytopenic purpura patients. [source] | |||||||||||||