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1.
气相中酶分子表面的水化层对其催化行为具有显著的影响。本文采用全原子分子动力学模拟方法考察了气相体系碳酸酐酶表面的水化层对酶结构以及CO2在酶分子中扩散行为的影响。首先展现了水分子在酶分子及其活性中心周围的分布,研究了水化层厚度对于酶结构以及CO2扩散速率的影响;发现最有利于CO2扩散进入酶分子的水化层厚度为0.7 nm。确认了碳酸酐酶内CO2的吸附位点,通过对其开合状态统计,显示出碳酸酐酶中CO2扩散通道中的瓶颈位置。上述结果对设计和优化碳酸酐酶催化气相体系中CO2的吸附和转化提供了依据和启示。 相似文献
2.
Saúl Gómez-Manzo Jaime Marcial-Quino America Vanoye-Carlo Hugo Serrano-Posada Abigail González-Valdez Víctor Martínez-Rosas Beatriz Hernández-Ochoa Edgar Sierra-Palacios Rosa Angélica Castillo-Rodríguez Miguel Cuevas-Cruz Eduardo Rodríguez-Bustamante Roberto Arreguin-Espinosa 《International journal of molecular sciences》2016,17(5)
Glucose-6-phosphate dehydrogenase (G6PD) deficiency in humans causes severe disease, varying from mostly asymptomatic individuals to patients showing neonatal jaundice, acute hemolysis episodes or chronic nonspherocytic hemolytic anemia. In order to understand the effect of the mutations in G6PD gene function and its relation with G6PD deficiency severity, we report the construction, cloning and expression as well as the detailed kinetic and stability characterization of three purified clinical variants of G6PD that present in the Mexican population: G6PD Zacatecas (Class I), Vanua-Lava (Class II) and Viangchan (Class II). For all the G6PD mutants, we obtained low purification yield and altered kinetic parameters compared with Wild Type (WT). Our results show that the mutations, regardless of the distance from the active site where they are located, affect the catalytic properties and structural parameters and that these changes could be associated with the clinical presentation of the deficiency. Specifically, the structural characterization of the G6PD Zacatecas mutant suggests that the R257L mutation have a strong effect on the global stability of G6PD favoring an unstable active site. Using computational analysis, we offer a molecular explanation of the effects of these mutations on the active site. 相似文献
3.
甲醛(HCHO)是一种主要的室内空气污染物,具有高致癌性和致突变性,催化氧化是一种理想而有效的室内消除甲醛的方法。二氧化钛作为载体负载贵金属催化剂在甲醛催化氧化反应中表现出优良的催化性能。本文综述了近年来二氧化钛基催化剂催化氧化甲醛的研究进展,主要总结了二氧化钛的吸附机理,二氧化钛晶体结构、表面形貌及微观结构、表面活性氧物种和还原性等对二氧化钛基负载贵金属催化剂催化氧化甲醛性能的影响,重点关注了催化剂的化学结构性质与甲醛氧化活性的关系,并归纳了一部分甲醛催化氧化反应机理。最后指出二氧化钛基催化剂在甲醛催化氧化反应中未来研究方向为:合理设计TiO2各种缺陷和晶面暴露,同时提高贵金属的分散性和原子利用效率,继而进一步提高催化剂的性能;在保持催化剂高活性、高稳定性的同时,推进设计实际应用整体式催化剂的研究进程。 相似文献
4.
Three in One: Temperature,Solvent and Catalytic Stability by Engineering the Cofactor‐Binding Element of Amine Transaminase
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Dr. Tim Börner Dr. Sebastian Rämisch Dr. Sebastian Bartsch Dr. Andreas Vogel Prof. Patrick Adlercreutz Assoc. Prof. Carl Grey 《Chembiochem : a European journal of chemical biology》2017,18(15):1482-1486
Amine transaminase (ATA) catalyse enantioselectively the direct amination of ketones, but insufficient stability during catalysis limits their industrial applicability. Recently, we revealed that ATAs suffer from substrate‐induced inactivation mechanism involving dissociation of the enzyme–cofactor intermediate. Here, we report on engineering the cofactor‐ring‐binding element, which also shapes the active‐site entrance. Only two point mutations in this motif improved temperature and catalytic stability in both biphasic media and organic solvent. Thermodynamic analysis revealed a higher melting point for the enzyme–cofactor intermediate. The high cofactor affinity eliminates the need for pyridoxal 5′‐phosphate supply, thus making large‐scale reactions more cost effective. This is the first report on stabilising a tetrameric ATA by mutating a single structural element. As this structural “hotspot” is a common feature of other transaminases it could serve as a general engineering target. 相似文献
5.
Different types of enzymes such as lipases, several phosphatases, dehydrogenases, oxidases, amylases and others are well suited for the reactions in SC-CO2. The stability and the activity of enzymes exposed to carbon dioxide under high pressure depend on enzyme species, water content in the solution and on the pressure and temperature of the reaction system. The three-dimensional structure of enzymes may be significantly altered under extreme conditions, causing their denaturation and consequent loss of activity. If the conditions are less adverse, the protein structure may be largely retained. Minor structural changes may induce an alternative active protein state with altered enzyme activity, specificity and stability. 相似文献
6.
Reactions of alkylene oxides with carbon dioxide underlie the industrial technology of ethylene- and propylene carbonates.
Looking for new catalytic systems for these processes remains of interest due to the possibility of creating a new energy-saving
process for the production of ethylene and propylene glycols. This work is aimed at comparing the catalytic activity of halogenides
in the reaction of propylene oxide (PO) and carbon dioxide in the presence of tetrasubstituted ammonium and phosphonium halogenides,
and evaluating the feasibility of using them in designing industrial technologies for the production of alkylene carbonates
and glycols as active catalytic systems. Triphenylphosphine halogenides have been shown to possess high catalytic activity
as compared to triethanolamine-based analogs. In terms of efficiency, triphenylphosphonium bromides are as good as the familiar
catalysts based on potassium iodide. The high activity of these catalysts in the reaction for propylene carbonate (PC) production
and their good solubility in the reaction medium allow us to propose them for the development of industrial technology for
the subsequent production of alkyl carbonates and alkylene glycols. 相似文献
7.
Yip SH Foo JL Schenk G Gahan LR Carr PD Ollis DL 《Protein engineering, design & selection : PEDS》2011,24(12):861-872
Directed evolution was used to enhance the activity of the glycerophosphodiesterase enzyme from Enterobacter aerogenes, GpdQ, toward bis(para-nitrophenol) phosphate (BpNPP), a substrate that is frequently used to assay phosphodiesterases. Native GpdQ has a low level of activity toward BpNPP while the evolved enzymes exhibited k(cat) values that were well over 100 times better while improvements in k(cat)/K(m) of around 500 times were observed along with improved activity we observed a change in the oligomeric structure in the evolved enzymes. The native enzyme is a hexamer with tightly associated dimers related by a 3-fold axis. The stability of the dimer was attributed in part to the cap domain that forms a disulfide bond with its 2-fold-related subunit and in part due to the fact that dimerization results in burying 23.6% of the monomer's accessible surface area. The cap domain also forms the top of the active site and contributes an essential part of the interface between 3-fold-related molecules. The evolved proteins quickly lost one of the cysteine residues that formed the disulfide bond and other mutations that might stabilize the cap domain. The likely effect of these mutations was to open up the active site for the new substrate and to favor the formation of dimeric molecules. The breakdown of the oligomeric structure was accompanied by a reduction in the thermal stability of the protein-as monitored by the residual activity of the native and mutant proteins following pre-incubation at elevated temperatures. A discussion on the evolutionary implications of these studies is presented. 相似文献
8.
The catalytic behaviour of potassium carbonate doped onto active carbon was investigated with respect to reduction of carbon dioxide. The distribution of potassium on the carbon surface was found by an X-ray microanalyzer to be uniform. The amount of oxygen trapped on the carbon surface during reaction was nearly proportional to the surface concentration of potassium. The catalytic activity with carbon doped with less than 2% potassium carbonate was proportional to the amount of trapped oxygen, while excessive doping by potassium was found to form trapped oxygen independently of the gasification of carbon. Disproportionation of carbon monoxide into carbon dioxide and carbon was found to take place readily at 700 °C, with carbon doped with 4.0 wt % potassium carbonate. 相似文献
9.
Site-directed mutagenesis study of a conserved residue in family 10 glycanases: histidine 86 of xylanase A from Streptomyces lividans 总被引:1,自引:0,他引:1
Roberge M; Shareck F; Morosoli R; Kluepfel D; Dupont C 《Protein engineering, design & selection : PEDS》1998,11(5):399-404
Xylanases from family 10 glycanases contain three conserved histidine
residues in their active site. The role of H86 in the structure- function
of xylanase A from Streptomyces lividans (XlnA) was studied by
site-directed mutagenesis. Six mutant proteins (H86A/E/F/K/Q/W) were
produced, purified and characterized. The six mutations reduced the
affinity of XlnA towards xylan without having any major effect on the
catalytic constant. All these mutations also lowered the pKa of the
acid-base catalyst by 0.46-1.94 pH units. The mutations decreased the
enzyme stability at 60 degrees C by up to 95% and the transition
temperature by 2.2-5.8 degrees C. Unfolding of the protein with guanidine
hydrochloride (GdnxHCl) showed that five out of six mutations decreased the
concentration required to denature 50% of the XlnA, confirming the
importance of H86 for the stability of the enzyme. The increase in m value
m=d(deltaG)/d[GdnxHCl] also suggested the involvement of residue H86 in the
structure of the denatured state of XlnA. It can be concluded from this
study that this active site residue was conserved in family 10 glycanases
for its function in maintaining the elevated pKa of the acid-base catalyst
and in the stability of the protein, while being of little importance for
the activity.
相似文献
10.
11.
采用碳纳米管增强复合材料催化剂,在等温积分反应器中获得环氧乙烷非均相催化水合宏观反应动力学实验数据,建立了幂函数型宏观反应动力学方程,采用Levenberg-Marquardt法对动力学模型参数进行估算,并以该动力学模型为基础,分析了均温反应器的热稳定性。结果表明,生成乙二醇主反应的表观活化能为71.7 k J/mol,与两个典型的串联副反应的活化能接近。模型参数统计检验结果表明,该宏观动力学方程参数是适定的,可用于工业反应器的设计。给出的反应器关键参数的计算方法,可为乙二醇合成反应器的模拟计算和设计开发提供必要的依据。 相似文献
12.
Yonemoto W; McGlone ML; Grant B; Taylor SS 《Protein engineering, design & selection : PEDS》1997,10(8):915-925
When the catalytic (rC) subunit of cAMP-dependent protein kinase (cAPK) is
expressed in Escherichia coli, it is autophosphorylated at four sites,
Ser10, Ser139, Ser338 and Thr197 (49). Three of these sites, Ser10, Ser338
and Thr197, are also found in the mammalian enzyme. To understand the
functional importance of these phosphorylation sites, each was replaced
with Ala, Glu or Asp. The expression, solubility and phosphorylation state
of each mutant protein was characterized by immunoprecipitation following
in vivo labeling with 32Pi. When possible, isoforms were resolved and
kinetic properties were measured. The two stable phosphorylation sites in
the mammalian enzyme, Ser338 and Thr197, were shown to play different
roles. Ser338, which stabilizes a turn near the C-terminus, is important
for stability. Both rC(S338A) and rC(S338E) were very labile; however, the
kinetic properties of rC(S338E) were similar to the wild-type catalytic
subunit (C-subunit). Ser338 most likely helps to anchor the C-terminus to
the surface of the small lobe. Thr197 is in the activation loop near the
cleft interface. Mutagenesis of T197 caused a significant loss of catalytic
activity with increases in Kms for both peptide and MgATP, as well as a
small decrease in k(cat) indicating that this phosphate is important for
the correct orientation of catalytic residues at the active site.
Replacement of Ser139, positioned at the beginning of the E-helix, with Ala
had no effect on the kinetic parameters, stability or phosphorylation at
the remaining sites. In contrast, mutation of Ser10, located at the
beginning of the A-helix, produced mostly insoluble, inactive,
unphosphorylated protein, suggesting that this region, though far removed
from the active site, is structurally important at least for the expression
of soluble phosphoprotein in E.coli. Since the mutation of active site
residues as well as deletion mutants generate underphosphorylated proteins,
these phosphorylations in E.coli all result from autophosphorylation.
相似文献
13.
It is widely agreed that new enzymes evolve from existing ones through the duplication of genes encoding existing enzymes followed by sequence divergence. While evolution is an inherently random process, studies of divergently related enzymes have shown that the evolution of new enzymes follows one of three general routes in which the substrate specificity, reaction mechanism, or active site architecture of the progenitor enzyme is reused in the new enzyme. Recent developments in structural biology relating to divergently related (beta/alpha)8 enzymes have brought new insight into these processes and have revealed that conserved structural elements play an important role in divergent evolution. These studies have shown that, although evolution occurs as a series of random mutations, stable folds such as the (beta/alpha)8 barrel and structural features of the active sites of enzymes are frequently reused in evolution and adapted for new catalytic purposes. 相似文献
14.
Douglas W. McKee 《Fuel》1983,62(2):170-175
The catalytic effects of alkali metal salts in the gasification of carbonaceous materials by oxygen, steam and carbon dioxide are described. The most effective catalysts are generally the carbonates, oxides and hydroxides; other active salts tend to convert to these species under gasification conditions. Current theories of the mechanism of this type of catalysis are reviewed. Thermodynamic considerations, the results of thermal analysis and the magnitude of kinetic isotope effects suggest that cyclic sequences of elementary reactions are responsible for the catalytic phenomena. 相似文献
15.
Jan M. Skowroski 《Fuel》1977,56(4):385-389
The relation between the morphological and the catalytic properties of active carbon-nickel catalysts was investigated in connection with using these catalysts as cathodes in air-zinc cells. The samples, containing different amounts of deposited nickel nitrate were activated in carbon dioxide. During the process of activation changes in texture porosity, surface area and helium density appeared. These properties are discussed in relation to the catalytic activity of the active carbon-nickel catalysts. It was found that the properties mentioned above may be modified according to the nickel content. The dispersion and the texture of nickel on the surface of active carbon were examined by scanning electron microscopy. 相似文献
16.
17.
Mutations Closer to the Active Site Improve the Promiscuous Aldolase Activity of 4‐Oxalocrotonate Tautomerase More Effectively than Distant Mutations
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Mehran Rahimi Jan‐Ytzen van der Meer Dr. Edzard M. Geertsema Harshwardhan Poddar Dr. Bert‐Jan Baas Prof. Dr. Gerrit J. Poelarends 《Chembiochem : a European journal of chemical biology》2016,17(13):1225-1228
The enzyme 4‐oxalocrotonate tautomerase (4‐OT), which catalyzes enol–keto tautomerization as part of a degradative pathway for aromatic hydrocarbons, promiscuously catalyzes various carbon–carbon bond‐forming reactions. These include the aldol condensation of acetaldehyde with benzaldehyde to yield cinnamaldehyde. Here, we demonstrate that 4‐OT can be engineered into a more efficient aldolase for this condensation reaction, with a >5000‐fold improvement in catalytic efficiency (kcat/Km) and a >107‐fold change in reaction specificity, by exploring small libraries in which only “hotspots” are varied. The hotspots were identified by systematic mutagenesis (covering each residue), followed by a screen for single mutations that give a strong improvement in the desired aldolase activity. All beneficial mutations were near the active site of 4‐OT, thus underpinning the notion that new catalytic activities of a promiscuous enzyme are more effectively enhanced by mutations close to the active site. 相似文献
18.
Strontium was supported on a variety of carriers, including silica, alumina, titania and carbon, by impregnation and decomposition
of an acetate precursor at 773 K. These supported samples were characterized by surface area measurements, stepwise temperature-programmed
desorption of carbon dioxide and activity for the catalytic decomposition of 2-propanol. In some cases, infrared and X-ray
absorption spectroscopy were used to identify surface species. Results from these techniques suggested that strontium supported
on silica forms a weakly basic surface silicate phase that had low activity for 2-propanol dehydrogenation. On alumina and
titania, strontium acetate decomposed to form supported basic carbonates that were moderately active for 2-propanol dehydrogenation.
When rates are normalized by the base site density determined from CO2 desorption, strontium supported on carbon was the most active sample for dehydrogenation of 2-propanol. These results suggest
that the nature of supported alkaline earth catalysts is strongly dependent on the composition of the carrier.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
《Catalysis communications》2002,3(3):119-123
Alumina/silica aerogel with zinc chloride alkylation catalyst, was obtained using one step sol–gel synthesis and subsequent drying with the supercritical carbon dioxide. The high density supercritical carbon dioxide drying conditions resulted in zinc chloride removal from the catalyst surface, surface area and pore volume increase and catalytic activity decrease. The low density supercritical carbon dioxide drying conditions, pore size distribution centred around 6 nm pore radius and high degree of mixed Al–O–Si bonds in the alumina/silica aerogel network, were found to increase the catalytic activity of the obtained aerogel catalysts. 相似文献
20.
Dr. Jorick Franceus Zorica Ubiparip Dr. Koen Beerens Prof. Dr. Tom Desmet 《Chembiochem : a European journal of chemical biology》2021,22(18):2777-2782
2-O-Glucosylglycerol is accumulated by various bacteria and plants in response to environmental stress. It is widely applied as a bioactive moisturising ingredient in skin care products, for which it is manufactured via enzymatic glucosylation of glycerol by the sucrose phosphorylase from Leuconostoc mesenteroides. This industrial process is operated at room temperature due to the mediocre stability of the biocatalyst, often leading to microbial contamination. The highly thermostable sucrose phosphorylase from Bifidobacterium adolescentis could be a better alternative in that regard, but this enzyme is not fit for production of 2-O-glucosylglycerol due to its low regioselectivity and poor affinity for glycerol. In this work, the thermostable phosphorylase was engineered to alleviate these problems. Several engineering approaches were explored, ranging from site-directed mutagenesis to conventional, binary, iterative or combinatorial randomisation of the active site, resulting in the screening of ∼3,900 variants. Variant P134Q displayed a 21-fold increase in catalytic efficiency for glycerol, as well as a threefold improvement in regioselectivity towards the 2-position of the substrate, while retaining its activity for several days at elevated temperatures. 相似文献