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Reversible Binding (reversible + binding)
Selected AbstractsTriphenylantimony(v) Catecholates and o -Amidophenolates: Reversible Binding of Molecular OxygenCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2006Vladimir K. Cherkasov Prof. Dr. Abstract Novel neutral antimony(V) complexes were isolated as crystalline materials and characterized by IR and NMR spectroscopy: o -amidophenolate complexes [4,6-di- tert -butyl- N -(2,6-dimethylphenyl)- o -amidophenolato]triphenylantimony(V) (Ph3Sb[AP-Me], 1) and [4,6-di- tert -butyl- N -(2,6-diisopropylphenyl)- o -amidophenolato]triphenylantimony(v) (Ph3Sb[AP- iPr], 2); catecholate complexes (3,6-di- tert -butyl-4-methoxycatecholato)triphenylantimony(V) (Ph3Sb[(MeO)Cat], 3), its methanol solvate 3,CH3OH (4); (3,6-di- tert -butyl-4,5-di-methoxycatecholato)triphenylantimony(V) (Ph3Sb[(MeO)2Cat], 5) and its acetonitrile solvate 5,CH3CN (6). Complexes 1,7 were synthesized by oxidative addition of the corresponding o -iminobenzoquinones or o -benzoquinones to Ph3Sb. In the case of the phenanthrene-9,10-diolate (PhenCat) ligand, two different complexes were isolated: Ph3Sb[PhenCat] (7) and [Ph4Sb]+[Ph2Sb(PhenCat)2], (8). Complexes 7 and 8 were found to be in equilibrium in solution. Molecular structures of 2, 4, 6, and 8 were determined by X-ray crystallography. Complexes 1,7 reversibly bind molecular oxygen to yield Ph3Sb[L-Me]O2 (9), Ph3Sb[L- iPr]O2 (10), Ph3Sb[(MeO)L,]O2 (11), Ph3Sb[(MeO)2L,]O2 (12) and Ph3Sb[PhenL,]O2 (13), which contain five-membered trioxastibolane species (where L is the O,O,,N-coordinated derivative of a 1-hydroperoxy-6-(N -aryl)-iminocyclohexa-2,4-dienol, and L, the O,O,,O,,-coordinated derivative of 6-hydroperoxy-6-hydroxycyclohexa-2,4-dienone). Complexes 9,13 were characterized by IR and 1H NMR spectroscopy and X-ray crystallography. [source] Characterization of the NAD+ binding site of Candida boidinii formate dehydrogenase by affinity labelling and site-directed mutagenesisFEBS JOURNAL, Issue 22 2000Nikolas E. Labrou The 2,,3,-dialdehyde derivative of ADP (oADP) has been shown to be an affinity label for the NAD+ binding site of recombinant Candida boidinii formate dehydrogenase (FDH). Inactivation of FDH by oADP at pH 7.6 followed biphasic pseudo first-order saturation kinetics. The rate of inactivation exhibited a nonlinear dependence on the concentration of oADP, which can be described by reversible binding of reagent to the enzyme (Kd = 0.46 mm for the fast phase, 0.45 mm for the slow phase) prior to the irreversible reaction, with maximum rate constants of 0.012 and 0.007 min,1 for the fast and slow phases, respectively. Inactivation of formate dehydrogenase by oADP resulted in the formation of an enzyme,oADP product, a process that was reversed after dialysis or after treatment with 2-mercaptoethanol (> 90% reactivation). The reactivation of the enzyme by 2-mercaptoethanol was prevented if the enzyme,oADP complex was previously reduced by NaBH4, suggesting that the reaction product was a stable Schiff's base. Protection from inactivation was afforded by nucleotides (NAD+, NADH and ADP) demonstrating the specificity of the reaction. When the enzyme was completely inactivated, approximately 1 mol of [14C]oADP per mol of subunit was incorporated. Cleavage of [14C]oADP-modified enzyme with trypsin and subsequent separation of peptides by RP-HPLC gave only one radioactive peak. Amino-acid sequencing of the radioactive tryptic peptide revealed the target site of oADP reaction to be Lys360. These results indicate that oADP inactivates FDH by specific reaction at the nucleotide binding site, with negative cooperativity between subunits accounting for the appearance of two phases of inactivation. Molecular modelling studies were used to create a model of C. boidinii FDH, based on the known structure of the Pseudomonas enzyme, using the modeller 4 program. The model confirmed that Lys360 is positioned at the NAD+ -binding site. Site-directed mutagenesis was used in dissecting the structure and functional role of Lys360. The mutant Lys360,Ala enzyme exhibited unchanged kcat and Km values for formate but showed reduced affinity for NAD+. The molecular model was used to help interpret these biochemical data concerning the Lys360,Ala enzyme. The data are discussed in terms of engineering coenzyme specificity. [source] Wet and Dry Adhesion Properties of Self-Selective Nanowire ConnectorsADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Hyunhyub Ko Abstract Here, the wet and dry adhesion properties of hybrid Ge/parylene nanowire (NW) connectors are examined. The ability of the NW connectors to bind strongly even under lubricating conditions, such as mineral oil, sheds light on the dominant role of van der Waals interactions in the observed adhesion. The superhydrophobic surface of the NW connectors enables the wet, self-cleaning of contaminant particles from the surface, similar to the lotus effect. In addition, the effect of NW length on the shear adhesion strength, repeated usability, and robustness of the connectors, all critical properties for applications that require reversible binding of components, is examined. [source] Roles of partly unfolded conformations in macromolecular self-assemblyGENES TO CELLS, Issue 1 2001Keiichi Namba From genes to cells there are many steps of hierarchical increments in building up complex frameworks that provide intricate networks of macromolecular interactions, through which cellular activities such as gene expression, signal processing, energy transduction and material conversion are dynamically organized and regulated. The self-assembly of macromolecules into large complexes is one such important step, but this process is by no means a simple aggregation of macromolecules with predefined, rigid complementary structures. In many cases the component molecules undergo either domain rearrangements or folding of disordered portions, which occurs only following binding to their correct partners. The partial disorder is used in some cases to prevent spontaneous assembly at inappropriate times or locations. It is also often used for finely tuning the equilibrium and activation energy of reversible binding. In other cases, such as protein translocation across membranes, an unfolded terminus appears to be the prerequisite for the process as an initiation signal, as well as the physical necessity to be taken into narrow channels. Self-assembly processes of viruses and bacterial flagella are typical examples where the induced folding of disordered chains plays a key role in regulating the addition of new components to a growing assembly. Various aspects of mechanistic roles of natively unfolded conformations of proteins are overviewed and discussed in this short review. [source] Pharmacokinetics of factors IX, recombinant human activated factor VII and factor XIIIHAEMOPHILIA, Issue 2006M.-C. POON Summary., There is now a volume of literature on the pharmacokinetics (PK) of coagulation factor concentrates, although the majority is on factor VIII (FVIII) and factor IX (FIX). PK of FIX and FVIII are different with FIX having a larger volume of distribution (Vdss), higher elimination clearance (CL), longer mean resident time (MRT) and longer terminal half-life (T1/2,,). Factor IX in vivo recovery (IVR) is also much shorter possibly due to reversible binding of FIX to the endothelium and possibly to platelets. There is considerable FIX PK variability between products (particularly between plasma-derived FIX and recombinant FIX), and between individuals. Important inter-individual factors leading to PK variability include age and body weight because plasma volume as a fraction of body weight decreases with increasing weight and hence age. Thus, IVR increases with body weight and hence age and is consequently lower in children than in adults. Absolute Vdss and CL increase linearly with body weight and age in children and adolescents, becoming stable in adults with more stable weight. Inter-individual variability also likely applies to other clotting factors, particularly to recombinant activated FVII (rFVIIa) but likely also to the less well studied factor XIII (FXIII). The former is known to have an extremely short T1/2,,, large Vdss, high CL, short MRT, whereas the latter has an extremely long T1/2,,, large Vdss, short CL and long MRT. Both are discussed in this article. Understanding of PK of specific clotting factors in individual patients is important in order to make decisions regarding appropriate dosage and dosage intervals to treat patients, and to allow by means of computer modelling the determination of dosage to achieve target trough level at various dosing intervals for patients undergoing prophylaxis. [source] Kinetics of the sulfate radical-mediated photo-oxidation of humic substancesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2008Pedro M. David Gara The kinetics of the aqueous phase reaction of sulfate radicals with commercial humic acids and with organic matter extracted from vermicompost (VC) was studied by flash-photolysis. The results can be interpreted by a mechanism that in a first step considers the reversible binding of the sulfate radicals by the humic substances. Both the bound and free sulfate radicals decay to oxidized products. From experiments performed with Aldrich humic acids in the temperature range from 283 to 303 K, the enthalpy change associated with the binding process was estimated to be ,(36 ± 11) kJ mol,1. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 40: 19,24, 2008 [source] Bleeding risk with AZD6140, a reversible P2Y12 receptor antagonist, vs. clopidogrel in patients undergoing coronary artery bypass grafting in the DISPERSE2 trialINTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 4 2009S. Husted Summary AZD6140, the first reversible oral P2Y12 receptor antagonist, exhibits greater and more consistent inhibition of platelet aggregation than the irreversible thienopyridine clopidogrel. As a result of its reversible effect, AZD6140 may pose less risk for bleeding when antiplatelet treatment cannot be stopped at least 5 days before coronary artery bypass graft (CABG) surgery or other invasive procedures. The Dose conflrmation Study assessing anti-Platelet Effects of AZD6140 vs. clopidogRel in NSTEMI (DISPERSE2) trial showed overall comparable bleeding rates with antiplatelet treatment with AZD6140 90 mg twice daily or 180 mg twice daily vs. clopidogrel 75 mg once daily in 984 patients with non-ST-elevation acute coronary syndromes. A post hoc exploratory analysis of bleeding outcomes in the subset of 84 patients undergoing CABG in DISPERSE2 suggests reduced risk for total bleeding (41% and 58% vs. 62%), all major bleeding (38% and 50% vs. 62%), and life-threatening bleeding (22% and 38% vs. 54%) with AZD6140 90 mg (n = 32) and 180 mg (n = 26) vs. clopidogrel (n = 26) respectively. Trends suggested that major bleeding rates were reduced with AZD6140 (combined groups) vs. clopidogrel when treatment was stopped , 5 days prior to surgery (39% vs. 63%, p = 0.15) but not when treatment was stopped > 5 days before surgery (50% vs. 60%). This observation is consistent with the reversible binding of AZD6140 to the P2Y12 receptor. Further prospective studies are planned to assess the relationship between this potential clinical benefit of AZD6140 and the reversibility of its antiplatelet effects. [source] A high-throughput protocol for extracting high-purity genomic DNA from plants and animalsMOLECULAR ECOLOGY RESOURCES, Issue 4 2008R. WHITLOCK Abstract DNA extraction techniques that employ the reversible binding of DNA to silica via chaotropic salts can deliver high-quality genomic DNA from plant and animal tissues, while avoiding the use of toxic organic solvents. Existing techniques that use this method are either prohibitively expensive, or are applicable to only a restricted set of taxa. Here we describe a cost-effective DNA extraction technique suitable for a wide range of plant and animal taxa that yields microgram quantities of high-molecular-weight genomic DNA at a throughput of 192 samples per day. Our technique is particularly robust for tissue samples that are insoluble or are rapidly discoloured or oxidized in standard DNA extraction buffers. We demonstrate the quality of DNA extracted using this method by applying the amplified fragment length polymorphism technique to plant species. [source] Modeling the Inhibitor Activity and Relative Binding Affinities in Enzyme-Inhibitor-Protein Systems: Application to Developmental Regulation in a PG-PGIP SystemBIOTECHNOLOGY PROGRESS, Issue 3 2004Wayne W. Fish Within a number of classes of hydrolytic enzymes are certain enzymes whose activity is modulated by a specific inhibitor-protein that binds to the enzyme and forms an inactive complex. One unit of a specific inhibitor-protein activity is often defined as the amount necessary to inhibit one unit of its target enzyme by 50 %. No objective quantitative means is available to determine this point of 50 % inhibition in crude systems such as those encountered during purification. Two models were derived: the first model is based on an irreversible binding approximation, and the second, or equilibrium, model is based on reversible binding. The two models were validated using the inhibition data for the polygalacturonase-polygalacturonase-inhibiting protein (PG-PGIP) system. Theory and experimental results indicate that the first model can be used for inhibitor protein activity determination and the second model can be used for inhibitor protein activity determination as well as for comparison of association constants among enzymes and their inhibitor-proteins from multiple sources. The models were used to identify and further clarify the nature of a differential regulation of expression of polygalacturonase-inhibiting protein in developing cantaloupe fruit. These are the first relations that provide for an objective and quantitative determination of inhibitor-protein activity in both pure and crude systems. Application of these models should prove valuable in gaining insights into regulatory mechanisms and enzyme-inhibitor-protein interactions. [source] Affinity Purification of Lipid VesiclesBIOTECHNOLOGY PROGRESS, Issue 1 2004Boris Peker We present a novel column chromatography technique for recovery and purification of lipid vesicles, which can be extended to other macromolecular assemblies. This technique is based on reversible binding of biotinylated lipids to monomeric avidin. Unlike the very strong binding of biotin and biotin-functionalized molecules to streptavidin, the interaction between biotin-functionalized molecules and monomeric avidin can be disrupted effectively by ligand competition from free biotin. In this work, biotin-functionalized lipids (biotin-PEG-PE) were incorporated into synthetic lipid vesicles (DOPC), resulting in unilamellar biotinylated lipid vesicles. The vesicles were bound to immobilized monomeric avidin, washed extensively with buffer, and eluted with a buffer supplemented with free biotin. Increasing the biotinyl lipid molar ratio beyond 0.53% of all lipids did not increase the efficiency of vesicle recovery. A simple adsorption model suggests 1.1 × 1013 active binding sites/mL of resin with an equilibrium binding constant of K = 1.0 × 108 M,1. We also show that this method is very robust and reproducible and can accommodate vesicles of varying sizes with diverse contents. This method can be scaled up to larger columns and/or high throughput analysis, such as a 96-well plate format. [source] Templated assembly of the pH-sensitive membrane-lytic peptide GALACHEMICAL BIOLOGY & DRUG DESIGN, Issue 6 2004D.H. Haas Abstract:, Delivery of protein or nucleic acid therapeutics into intracellular compartments may require facilitation to allow these macromolecules to cross otherwise impermeant cellular membranes. Peptides capable of forming membrane-spanning channels hold promise as just such facilitators, although the requirement for peptide oligomerization to form these channels may limit their effectiveness. Synthetic molecules containing multiple copies of membrane-active peptides attached to a template molecule in a pre-oligomerized form have attracted interest for drug-delivery applications. Using three template designs, we synthesized multimeric versions of the pH-sensitive lytic peptide GALA and compared their performance to monomeric GALA. Template assembly stabilized helix formation: templated GALA retained , -helical structure even at neutral pH, unlike monomeric GALA. In membrane leakage assays, templated GALA retained the pH sensitivity of the monomer, with improved leakage for dimeric GALA. Surprisingly, trimeric GALA was less effective, particularly when synthesized with a larger and more flexible spacer. Surface plasmon resonance analysis indicated that reversible binding of templated GALA to lipid surfaces at acidic conditions was greatly reduced compared with monomeric GALA, but that the amount of irreversibly bound material was similar. We interpreted these results to indicate that templated peptides may cyclize into ,self-satisfied' oligomeric structures, incapable of further aggregation and subsequent pore formation. Future design of templated peptides must be carefully performed to avoid this unwanted consequence. [source] | ||||||||||||||||