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Inhibition Mechanism (inhibition + mechanism)
Selected AbstractsInhibition Mechanism of TbIII on Horseradish Peroxidase ActivityCHEMISTRY & BIODIVERSITY, Issue 10 2008Shaofen Guo Abstract The inhibition mechanism of TbIII on horseradish peroxidase (HRP) in vitro was discussed. The results from MALDI-TOF/MS and X-ray photoelectron spectroscopy (XPS) showed that TbIII mainly interacts with the O-containing groups of the amides in the polypeptide chains of the HRP molecules and forms the complex of TbIII,HRP, and, in the complex, the molar ratio TbIII/HRP is 2,:,1. The results from CD and atomic force microscopy (AFM) indicated that the coordination effect between TbIII and HRP can lead to the conformation change in the HRP molecule, in which the contents of , -helix and , -sheet conformation in the peptide of the HRP molecules is decreased, and the content of the random coil conformation is increased. Meanwhile, the coordination effect also leads to the decrease in the content of inter- and intrapeptide-chain H-bonds in the HRP molecules, resulting in the HRP molecular looseness and/or aggregation. Thus, the conformation change in the HRP molecules can significantly decrease the electrochemical reaction of HRP and its electrocatalytic activity for the reduction of H2O2. [source] Young children who abandon error behaviourally still have to free themselves mentally: a retrospective test for inhibition in intuitive physicsDEVELOPMENTAL SCIENCE, Issue 3 2004Norman H. Freeman When preschoolers overcome persistent error, subsequent patterns of correct choices may identify how the error had been overcome. Children who no longer misrepresented a ball rolling down a bent tube as though it could only fall vertically, were asked sometimes to approach and sometimes to avoid where the ball landed. All children showed requisite task-switching flexibility. The pattern of 4-year-olds' correct choices among different places showed unnecessary avoidance of any place that would previously have tempted them into a vertical-approach error, 5-year-olds rebounded into a reversal, and 7-year-olds were flexible. The data attest to an inhibition mechanism, ruling out competing possibilities. [source] Combined use of chiral ionic liquid and CD for MEKC: Part II.ELECTROPHORESIS, Issue 16 2009Determination of binding constants Abstract A competitive inhibition mechanism is proposed to investigate the interactions among 2,3,6-tri- O -methyl-,-CD (TM-,-CD), cationic ionic liquid type surfactants, N -undecenoxy-carbonyl- L -leucinol bromide (L -UCLB) and profens using affinity CE. The apparent binding constant of TM-,-CD to L -UCLB was estimated by nonlinear and linear plotting methods. The binding constants of one representative profen (e.g. fenoprofen) to TM-,-CD and L -UCLB were estimated by a secondary plotting approach. The R - and S -fenoprofens have different binding constant values, resulting in the enantioseparation due to the synergistic effect of the two chiral selectors, TM-,-CD and L -UCLB. [source] Functional importance of Asp37 from a family 11 xylanase in the binding to two proteinaceous xylanase inhibitors from wheatFEMS MICROBIOLOGY LETTERS, Issue 1 2004Tariq A. Tahir Abstract Aspergillus niger xylanase is a target enzyme of the two wheat proteinaceous inhibitors, XIP-I and TAXI-I. We previously suggested that the xylanase "thumb" region was XIP-I binding site. Here, we expressed the Asp37Ala mutant in Pichia pastoris and showed that the mutation abolished the enzyme capacity to interact with both inhibitors, suggesting a direct contact at the active site. The mutant pH profile was altered, confirming the key role of Asp37 in determining the pH optima of glycoside hydrolase family 11. The results are consistent with a competitive inhibition mode and underline the strategic importance of Asp37 in the inhibition mechanism. [source] Immunosuppression using the mTOR inhibition mechanism affects replacement of rat liver with transplanted cells,HEPATOLOGY, Issue 2 2006Yao-Ming Wu Successful grafting of tissues or cells from mismatched donors requires systemic immunosuppression. It is yet to be determined whether immunosuppressive manipulations perturb transplanted cell engraftment or proliferation. We used syngeneic and allogeneic cell transplantation assays based on F344 recipient rats lacking dipeptidyl peptidase IV enzyme activity to identify transplanted hepatocytes. Immunosuppressive drugs used were tacrolimus (a calcineurin inhibitor) and its synergistic partners, rapamycin (a regulator of the mammalian target of rapamycin [mTOR]) and mycophenolate mofetil (an inosine monophosphate dehydrogenase inhibitor). First, suitable drug doses capable of inducing long-term survival of allografted hepatocytes were identified. In pharmacologically effective doses, rapamycin enhanced cell engraftment by downregulating hepatic expression of selected inflammatory cytokines but profoundly impaired proliferation of transplanted cells, which was necessary for liver repopulation. In contrast, tacrolimus and/or mycophenolate mofetil perturbed neither transplanted cell engraftment nor their proliferation. Therefore, mTOR-dependent extracellular and intracellular mechanisms affected liver replacement with transplanted cells. In conclusion, insights into the biological effects of specific drugs on transplanted cells are critical in identifying suitable immunosuppressive strategies for cell therapy. (HEPATOLOGY 2006;44:410,419.) [source] Thermodynamic micellization model for asphaltene precipitation inhibitionAICHE JOURNAL, Issue 2 2000Huanquan Pan Aromatic solvents and oil-soluble amphiphiles are recognized as asphaltene precipitation inhibitors in oil production and transportation. In the absence of the model describing the effect of these inhibitors on asphaltene precipitation from crudes, proposed is a thermodynamic micellization model explaining the inhibition mechanism for both aromatic solvents and oil-soluble amphiphiles. The model shows that aromatic solvents are concentrated in the micellar shell, and the interfacial tension between the asphaltene micellar core and shell is reduced as the micelles becomes stabler. A crude, mixed with a small amount of an oil-soluble amphiphile, achieves a high micellar stability. The amphiphiles behave like resin species of the crude and coadsorb onto the micellar core with resins. The adsorption enthalpy of an amphiphile onto the micellar core is much higher than that of the resin and, therefore, amphiphiles can be very effective inhibitors. The results suggest that the adsorption enthalpy data can be used to screen the amphiphiles for asphaltene precipitation inhibition. For a given oil-soluble amphiphile, this model can predict the amount of the amphiphile required to inhibit the precipitation. [source] Specificity and reactive loop length requirements for crmA inhibition of serine proteasesPROTEIN SCIENCE, Issue 2 2005Lisa D. Tesch Abstract The viral serpin, crmA, is distinguished by its small size and ability to inhibit both serine and cysteine proteases utilizing a reactive loop shorter than most other serpins. Here, we characterize the mechanism of crmA inhibition of serine proteases and probe the reactive loop length requirements for inhibition with two crmA reactive loop variants. P1 Arg crmA inhibited the trypsin-like proteases, thrombin, and factor Xa, with moderate efficiencies (,102,104 M,1sec,1), near equimolar inhibition stoichiometries, and formation of SDS-stable complexes which were resistant to dissociation (kdiss ,10,7 sec,1), consistent with a serpin-type inhibition mechanism. Trypsin was not inhibited, but efficiently cleaved the variant crmA as a substrate (kcat/KM of ,106 M,1 sec,1). N-terminal sequencing confirmed that the P1 Arg,P1,Cys bond was the site of cleavage. Altering the placement of the Arg in a double mutant P1 Gly-P1,Arg crmA resulted in minimal ability to inhibit any of the trypsin family proteases. This variant was cleaved by the proteases ,10-fold less efficiently than P1 Arg crmA. Surprisingly, pancreatic elastase was rapidly inhibited by wild-type and P1 Arg crmAs (105,106 M,1sec,1), although with elevated inhibition stoichiometries and higher rates of complex dissociation. N-terminal sequencing showed that elastase attacked the P1,Cys,P2,Ala bond, indicating that crmA can inhibit proteases using a reactive loop length similar to that used by other serpins, but with variations in this inhibition arising from different effective P2 residues. These results indicate that crmA inhibits serine proteases by the established serpin conformational trapping mechanism, but is unusual in inhibiting through either of two adjacent reactive sites. [source] Use of Dye Affinity Chromatography for the Purification of Aerococcusviridans Lactate OxidaseBIOTECHNOLOGY PROGRESS, Issue 3 2002Sergio A. Streitenberger Lactate oxidase was purified from Aerococcus viridans ( A. viridans) by dye affinity chromatography and FPLC ion exchange chromatography. The lactate oxidase could be purified by comparatively simple procedures, the purification achieved from a crude extract of A.viridans was 41-fold with a specific activity of 143 units/(mg of protein). The purified enzyme was a l - lactate oxidase, which catalyses the conversion of l -lactate in the presence of molecular oxygen to pyruvate and H2O2. This purified lactate oxidase showed an apparent molecular mass of 48 200 in SDS-PAGE and the native molecular weight, as estimated by FPLC gel filtration, was 187 300. This molecular weight indicates that lactate oxidase exists in tetrameric form after gel filtration. To differing degrees, all the triazine dyes tested were inhibitors of lactate oxidase, solutions of free triazine dyes showing an inhibition mechanism which was both time- and pH-dependent. [source] Kinetics and thermodynamics of glucoamylase inhibition by lactate during fermentable sugar production from food wasteJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2010Xiao Qiang Wang Abstract BACKGROUND: Glucoamylase hydrolysis is a key step in the bioconversion of food waste with complicated composition. This work investigated the effect of lactate on glucoamylase from Aspergillus niger UV-60, and inhibition mechanisms of glucoamylase by lactate during food waste hydrolysis. RESULTS: For 125 min hydrolysis of food waste (10%, dry basis), reducing sugars produced in the absence of lactate were 15%, 26% and 56% more than those produced in the presence of 24 g L,1 lactate at 60, 50 and 40 °C, respectively. Kinetic study showed that the type of glucoamylase inhibition by lactate was competitive, and Km (Michaelis-Menten constent), Vmax (maximum initial velocity), KI (inhibition constant) were 103.2 g L,1, 5.0 g L,1 min,1, 100.6 g L,1, respectively, for food waste hydrolysis at 60 °C and pH 4.6. Lactate also accelerated glucoamylase denaturation significantly. Activation energy of denaturation without inhibitor was 61% greater than that of denaturation with inhibitor (24 g L,1 lactate). Half-lives (t1/2) without inhibitor were 7.6, 2.7, 2.6, 1.7 and 1.2 times longer than those with inhibitor at temperature 40, 45, 50, 55 and 60 °C, respectively. CONCLUSION: These results are helpful to process optimization of saccharification and bioconversion of food waste. Copyright © 2010 Society of Chemical Industry [source] Rho-associated kinase (ROCK) inhibitor, Y27632, promotes neurite outgrowth in PC12 cells in the absence of NGFJOURNAL OF NEUROCHEMISTRY, Issue 2002R. Nath Neurite extension and retraction are very important processes in the formation of neuronal networks. A strategy for fostering axonal regrowth/regeneration of injured adult neurons is attractive therapeutically for various diseases such as traumatic brain injury, stroke and Alzheimer's disease. The Rho family of small GTPases, including Rac and Cdc42 have been shown to be involved in promoting neurite outgrowth. On the other hand, activation of RhoA induces collapse of growth cone and retraction of neurites. Rho-associated kinase (ROCK) an effector molecule of RhoA, is downstream of a number of axonal outgrowth and growth cone collapse inhibition mechanisms. In the present study, we sought to identify the role of ROCK in neurite outgrowth in PC12 cells. Y27632, a specific inhibitor of ROCK, induced a robust increase in neurite outgrowth in these cells within 24,48 h as visualized by phase contrast microscopy. Staining with FITC-tubulin or phalloidin show extended neurites in PC12 cells treated with Y27632, comparable to that with 100 ng/mL of NGF. Assessment of other biochemical markers of neurite outgrowth such as GAP43, neurofilament and tyrosine hydroxylase phosphorylation further indicates that inhibition of ROCK in PC12 cells causes differentiation of these cells to a neuronal phenotype. [source] Establishment of a quantitative structure,activity relationship model for evaluating and predicting the protective potentials of phenolic antioxidants on lipid peroxidationJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2003Zhiyong Cheng Abstract Antioxidant activities of phenolic compounds have been extensively explored, but the determinant factors underlying their mechanisms of action remain to be elucidated. In the present work, a series of phenolic compounds (hydroxylated connamic, benzoic acid, and polyphenol) were studied for their protection against lipid peroxidation (LPO) in two model experiments, pre-emulsified linoleic acid system and phosphate buffered linolenic acid system. The mechanisms of action as well as activity determinants were investigated by computational chemistry and multiple-linear regression analysis. Upon elucidating the LPO inhibition properties and the relationship between their structural natures and antioxidant activities (SAR), a fairly satisfactory multidescriptor quantitative SAR model was derived, which extended our understanding of LPO inhibition mechanisms and should be valuable in assessing or predicting the anti-LPO activity of phenolic antioxidants. © 2003 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 92:475,484, 2003 [source] Investigation of Catalytic Chain Transfer Copolymerization of MethacrylatesMACROMOLECULAR REACTION ENGINEERING, Issue 5 2008Anatoly N. Nikitin Abstract Batch experiments were carried out to investigate the kinetics of catalytic chain transfer copolymerization of methyl methacrylate and n -butyl methacrylate. The Predici® model developed to represent the system describes the numerous experimental data measured at high concentrations of Co(II) catalyst, taking into account the chain-length dependencies of termination, propagation and catalytic chain transfer. The constants for catalytic chain transfer are determined as 2.3,×,104 for both methyl methacrylate and n -butyl methacrylate from fitting the experimental data. Two inhibition mechanisms are shown to describe the decrease of the polymerization rate in the presence of catalyst equally well, with an unknown impurity dissolved in initiator introduced to explain experimental profiles measured at high initiator concentrations. [source] Instrumental analysis of gas hydrates propertiesASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010Y. Rojas Abstract Gas hydrates attracted intense research interest when it was first recognised some 70 years ago that they were responsible for the blockage of flow lines, valves and well heads, thereby causing great loss of production and other severe safety hazards to the oil and gas industry. After many decades, these compounds are still the topic of research activities in various multi-disciplinary fields, including chemical and petroleum engineering, earth and geophysics, chemistry and environmental sciences. This is not only due to the great impact that these compounds have on the oil and gas industry, but also to the potential applications they have in many evolving areas, including, but not only, natural gas storage and transportation, carbon dioxide sequestration, and sea-water desalination. It is generally accepted that gas hydrates represent the largest source of hydrocarbons on earth, something which has not been appreciated until only recently. Management, either prevention or application or both, of gas hydrates requires a complete knowledge and understanding of the formation, decomposition and inhibition mechanisms of gas hydrates, which in turn demands advanced experimental methods and instrumental techniques for gas hydrate characterisation. This paper reviews a broad range of techniques that have been used for natural gas hydrate characterisation. It includes the basic physical science principles of each method and the gas hydrate properties that each method is capable of detecting, including some modern instrumental analyses that enable direct determination of gas hydrate phases and possible measurement of molecular interactions within the fluid phases. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | |||||||||||||