The purpose of this study was to compare the effects of implant inclinations and load times on stress distributions in the peri-implant bone based on immediate- and delayed-loading models. Four 3D FEA models with different inclination angle of the posterior implants (0°, 15°, 30°, 45°) were constructed. A static load of 150?N in the multivectoral direction was applied unilaterally to the cantilever region. The stress distributions in the peri-implant bone were evaluated before and after osseointegration. The principal tensile stress (σmax), mean principal tensile stress (σmax), principal compressive stress (σmin) and mean principal compressive stress (σmin) of the bone and micromotion at the contact interface between the bone and implants were calculated. In all the models, peak principal stresses occurred in the bone surrounding the left tilted implant. The highest σmax and σmin were all observed in the 0° model for both immediate- and delayed-loading models. And the 0° and 15° models showed higher σmax and σmin values. The 0°models showed the largest micromotion. The observed stress distribution was better in the 30° and 45° models than in the 0° and 15° models. 相似文献
The effects on Robinia pseudoacacia (an exotic and invasive plant in Japanese rivers) of local scouring and saturation of the soil in the root-anchoring zone due to flooding were investigated. Scouring has been defined as the removal of substrate in the root-anchoring zone, exposing the tree roots. Tree-pulling experiments were conducted, simulating flood action, and the resulting damage was examined in order to assess the effect of local scouring on the maximum resistive bending moment (Mmax) for overturning. Scouring was artificially created to three different depths, 0, 25, and 50 cm. A nonlinear model was developed that included soil strength characteristics to calculate the critical overturning moment (Mcri) under dry and saturated soil conditions. Significant correlations (p < 0.05) of Mmax with different tree and root–soil plate characteristics, such as diameter at breast height (Dbh), tree weight, root depth, and root–soil plate radius, were developed in order to elucidate the effects of scouring on Mmax. Mmax was slightly reduced with scouring depth for trees with Dbh <10 cm (small) trunks, and it was significantly and negatively (p < 0.05) correlated with scouring depth for trees with 10 < Dbh < 20 cm (medium) trunks. However, Mmax did not change significantly with scouring depth for trees with a Dbh >20 cm (big) trunks. The nonlinear model was useful for determining the Mcri of R. pseudoacacia under dry and saturated soil conditions. The overturning moments of all (small, medium, and big) trees were considerably reduced under the saturated soil condition. It could be concluded that medium-sized trees were greatly affected by scouring, and that small and big trees were mainly affected by saturation of the soil under severe flooding conditions. 相似文献
Stalk bending strength (SBS) is a reliable indicator for evaluating stalk lodging resistance of maize plants. Based on biomechanical considerations, the maximum load exerted to breaking (Fmax), the breaking moment (Mmax) and critical stress (σmax) are three important parameters to characterize SBS. We investigated the genetic architecture of SBS by phenotyping Fmax, Mmax and σmax of the fourth internode of maize plants in a population of 216 recombinant inbred lines derived from the cross B73 × Ce03005 evaluated in four environments. Heritability of Fmax, Mmax and σmax was 0.81, 0.79 and 0.75, respectively. Fmax and σmax were positively correlated with several other stalk characters. By using a linkage map with 129 SSR markers, we detected two, three and two quantitative trait loci (QTL) explaining 22.4, 26.1 and 17.2 % of the genotypic variance for Fmax, Mmax and σmax, respectively. The QTL for Fmax, Mmax and σmax located in adjacent bins 5.02 and 5.03 as well as in bin 10.04 for Fmax were detected with high frequencies in cross-validation. As our QTL mapping results suggested a complex polygenic inheritance for SBS-related traits, we also evaluated the prediction accuracy of two genomic prediction methods (GBLUP and BayesB). In general, we found that both explained considerably higher proportions of the genetic variance than the values obtained in QTL mapping with cross-validation. Nevertheless, the identified QTL regions could be used as a starting point for fine mapping and gene cloning. 相似文献
doi: 10.1111/j.1741‐2358.2012.00653.x Prevalence of removable partial dentures users treated at the Aracatuba Dental School – UNESP Objectives: The aim of this study was to evaluate the frequency of removable partial dentures (RPD) at the Aracatuba Dental School. Methods: The study was conducted by analysing 412 clinical history of patients attended at the RPD clinics in the period from 2000 to 2007. Results: 412 charts were analysed: 148 (35.9%) men and 264 (64.1%) women. The mean age was 53.8 years (men) and 52.4 years (women). A total of 556 dentures were made; of these, 233 (41.90%) were maxillary and 323 (58.09%) were mandibular dentures. The most frequent Kennedy classification found was Class III (maxilla) and Class I (mandible). In the maxilla, 55% (126) of the major connectors were of the anterior–posterior palatal bar, while in the mandible, 64% (202) were the lingual bar. As regards the claps, 401 were circumferential and 318 were bar claps. Conclusion: The mean age of the patients was 52.9 years with higher prevalence of female patients; the most frequent Kennedy’s classification was Class I in mandible and Class III in maxilla; the most common major connector was anterior–posterior palatal bar for maxilla and lingual bar for mandible; the circumferential clasps were the most common retainer used in both jaws. 相似文献
In this review we collected data on the length at maturity (Lm) and maximum reported total length (Lmax) of 565 Mediterranean marine fish stocks, representing 150 species, 68 families, 24 orders and 3 classes. Overall, Lm ranged from 2 cm, for the males of the toothcarp Aphanius fasciatus, to 350 cm, for the females of the bluntnose sixgill shark Hexanchus griseus. Lm was positively linearly related with Lmax for Actinopterygii (logLm = ?0.123 + 0.92 × logLmax; r2 = 0.87, n = 471, P < 0.001) and Elasmobranchii (logLm = ?0.008 + 0.922 × logLmax; r2 = 0.90, n = 92, P < 0.001) with the two slopes being significantly different (ANCOVA: F = 2,904, P < 0.001). The reproductive load (Lm/Lmax) ranged between 0.23 (sand steenbras Lithognathus mormyrus) and 0.94 (angular roughshark Oxynotus centrina and thornback ray Raja clavata). The mean Lm/Lmax was significantly (ANOVA, F = 34.14, P < 0.001) lower for Actinopterygii (mean = 0.59, SD = 0.122, n = 471) compared to Elasmobranchii (mean = 0.70, SD = 0.132, n = 92) and Holocephali (mean = 0.77, SD = 0.077, n = 2). The Lm/Lmax was significantly (ANOVA, F = 43.80, P < 0.001) higher for species providing some form of parental care, i.e. guarders, bearers, nesters (mean Lm/Lmax ± SD = 0.68 ± 0.141, n = 111) compared to non-guarders (mean Lm/Lmax ± SD = 0.59 ± 0.123, n = 454). The mean Lm/Lmax displayed a remarkable constancy with longitude (northern and southern Mediterranean coastline: ANOVA, F = 0.01, P = 0.93), latitude (western, central and eastern regions: ANOVA, F = 1.25, P = 0.29) and habitat (ANOVA, F = 0.85, P = 0.51). 相似文献
The bis(heptalene)dimetal complexes (C12H10)2M2 of the first row transition metals from Ti to Ni are predicted by density functional theory to exhibit “submarine” sandwich structures with a pair of metal atoms sandwiched between the two heptalene rings. For the early transition metal derivatives (C12H10)2M2 (M = V, Cr) there are two types of such structures. In one structural type the metals are sandwiched between two heptahapto heptalene rings with metal-metal distances (3.5–3.8 Å) too long for direct metal-metal bonding. The other type of (C12H10)2M2 (M = V, Cr, Mn) structure has a pair of bonded metal atoms sandwiched between a fully bonded heptalene ligand and a heptalene ligand bonded to the metals only through an eight-carbon heptafulvene subunit, leaving an uncomplexed cis-1,3-diene unit. The formal metal-metal bond orders in these latter structures are 3, 2, and 1 for M = V, Cr, and Mn with predicted bond lengths of 2.5, 2.7, and 2.8 Å, respectively. For (C12H10)2Fe2 a singlet structure with each iron atom sandwiched between a hexahapto and a tetrahapto heptalene ring is energetically preferred over an alternate structure with ferrocene-like iron atoms sandwiched between two pentahapto heptalene rings. Partial bonding of each heptalene ring to the metal atoms occurs in the late transition metal derivatives (C12H10)2M2 (M = Co, Ni). This leads to an unsymmetrical structure for the cobalt derivative and a structure for the nickel derivative with each nickel atom sandwiched between a trihapto ligand and a tetrahapto ligand.
Figure
The bis(heptalene) dimetal complexes (C12H10)2M2 (M = Ti to Ni) are predicted by density functional theory to have a “submarine” sandwich structure with a pair of metal atoms sandwiched between the two heptalene rings. In the early transition metal derivatives (C12H10)2M2 (M = V, Cr) the metal atoms are sandwiched between two heptahapto heptalene rings. In contrast, for (C12H10)2M2 (M = Mn, Fe, Co, Ni) the heptalene rings are only partially bonded to the metal atoms. 相似文献
Hexavalent chromium contamination is a serious problem due to its high toxicity and carcinogenic effects on the biological systems. The enzymatic reduction of toxic Cr(VI) to the less toxic Cr(III) is an efficient technology for detoxification of Cr(VI)-contaminated industrial effluents. In this regard, a chromate reductase enzyme from a novel Ochrobactrum sp. strain Cr-B4, having the ability to detoxify Cr(VI) contaminated sites, has been partially purified and characterized. The molecular mass of this chromate reductase was found to be 31.53 kD, with a specific activity 14.26 U/mg without any addition of electron donors. The temperature and pH optima for chromate reductase activity were 40°C and 8.0, respectively. The activation energy (Ea) for the chromate reductase was found to be 34.7 kJ/mol up to 40°C and the activation energy for its deactivation (Ed) was found to be 79.6 kJ/mol over a temperature range of 50–80°C. The frequency factor for activation of chromate reductase was found to be 566.79 s?1, and for deactivation of chromate reductase it was found to be 265.66 × 103 s?1. The reductase activity of this enzyme was affected by the presence of various heavy metals and complexing agents, some of which (ethylenediamine tetraacetic acid [EDTA], mercaptoethanol, NaN3, Pb2+, Ni2+, Zn2+, and Cd2+) inhibited the enzyme activity, while metals like Cu2+ and Fe3+ significantly enhanced the reductase activity. The enzyme followed Michaelis–Menten kinetics with Km of 104.29 µM and a Vmax of 4.64 µM/min/mg. 相似文献
In order to find the susceptibility of the amino-Claisen rearrangement and the next proton shift reaction of N-allyl-N-arylamine to the substituent effects in the para position, the kinetic and thermodynamic parameters were calculated at the B3LYP level using the 6-31G** basis set. The calculated activation energies for the rearrangements and proton shift reactions are close to 44.4 and 49.5 kcal mol? 1, respectively. The transition states of the rearrangement with electron-donor substituents are more stable than those with electron-withdrawing substituent groups, but for the proton shift reaction, this situation is reversed (with the exception of fluorine atom for the rearrangement and fluorine and chlorine atoms for the proton shift reaction). Negative values for the activation entropy confirm the concerted mechanism for the amino-Claisen rearrangement and proton shift reaction. The Hammett ρ values of ? 2.4172 and ? 1.7791 are obtained for σp and σ? (enhanced sigma) in the amino-Claisen rearrangement, respectively. The correlation between log(kX/kH) and σp is weaker than that with σ? (enhanced sigma). A negative Hammett ρ value indicates that the electron-donating groups slightly increase the rate of amino-Claisen rearrangement. A positive Hammett ρ value (2.4921) for the proton shift reaction indicates that electron-withdrawing groups increase the rate of reaction. 相似文献
Ca-polygalacturonate is a demethoxylated component of pectins which are constitutive of plant root mucigel. In order to define the role of root mucigel in myrosinase immobilization and activity at root level, a myrosinase enzyme which had been isolated from Sinapis alba seeds was immobilized into Ca-polygalacturonate. The activity profile for the immobilized and free enzyme was evaluated using the pH-Stat method as a function of time, temperature, and pH. The Michaelis-Menten kinetic parameters change between the immobilized (Vmax?=?127?±?13 U mg?1 protein; KM?=?6.28?±?0.09?mM) and free (Vmax?=?17?±?1 U mg?1 protein; KM?=?0.96?±?0.01?mM) forms of myrosinase, probably due to conformational changes involving the active site as a consequence of enzyme immobilization. Immobilized enzyme activity evaluated as a function of different substrates gave the highest value with nasturtin, the glucosinolate that is typical of several brassicaceae plant roots containing the glucosinolate-myrosinase defensive system. No feedback regulation mechanism was found in the presence of an excess of enzymatic reaction products (i.e. allyl isothiocyanate or sulphate). The high enzyme immobilization yield into Ca-polygalacturonate and its activity preservation under different conditions suggest that the enzyme released by plants at root level could be entrapped in root mucigel in order to preserve its activity. 相似文献
The stimulation by Mg2+, Na+, K+, NH4+, and ATP of (Na+, K+)-ATPase activity in a gill microsomal fraction from the freshwater prawn Macrobrachium rosenbergii was examined. Immunofluorescence labeling revealed that the (Na+, K+)-ATPase α-subunit is distributed predominantly within the intralamellar septum, while Western blotting revealed a single α-subunit isoform of about 108 kDa Mr. Under saturating Mg2+, Na+, and K+ concentrations, the enzyme hydrolyzed ATP, obeying cooperative kinetics with VM = 115.0 ± 2.3 U mg?1, K0.5 = 0.10 ± 0.01 mmol L?1. Stimulation by Na+ (VM = 110.0 ± 3.3 U mg?1, K0.5 = 1.30 ± 0.03 mmol L?1), Mg2+ (VM = 115.0 ± 4.6 U mg?1, K0.5 = 0.96 ± 0.03 mmol L?1), NH4+ (VM = 141.0 ± 5.6 U mg?1, K0.5 = 1.90 ± 0.04 mmol L?1), and K+ (VM = 120.0 ± 2.4 U mg?1, KM = 2.74 ± 0.08 mmol L?1) followed single saturation curves and, except for K+, exhibited site–site interaction kinetics. Ouabain inhibited ATPase activity by around 73 % with KI = 12.4 ± 1.3 mol L?1. Complementary inhibition studies suggest the presence of F0F1–, Na+-, or K+-ATPases, but not V(H+)- or Ca2+-ATPases, in the gill microsomal preparation. K+ and NH4+ synergistically stimulated enzyme activity (≈25 %), suggesting that these ions bind to different sites on the molecule. We propose a mechanism for the stimulation by both NH4+, and K+ of the gill enzyme. 相似文献
doi: 10.1111/j.1741‐2358.2011.00572.x Compressive strains and displacement in a partially dentate lower jaw rehabilitated with two different treatment modalities Background: Understanding of the biomechanical consequences of the stresses generated to the supporting bone during occlusal loading is significant for improving the design and clinical planning process in partial edentulism therapy. Objective: The aim of this study was to analyse the distribution of strain and displacement on the partially dentate lower jaw rehabilitated with an partial denture (RPD) and to compare it to the strain and displacement distribution on a partially dentate lower jaw rehabilitated with a cantilever fixed partial denture (FPD). Material and methods: The experimental models were a partially dentate mandible with full‐arch PFM crowns and RPD and a partially dentate mandible rehabilitated with a full‐arch cantilever FPD. Strains and displacement were measured using the Digital Image Correlation Method. Results: Displacement values of the first experimental model ranged from 0.31 to 0.54 mm with strains from 1.35 to 2.34%. Analysis of the second experimental model results showed displacement values from 0 to 0.34 mm, while strains were in the range of 0–1.40%. Conclusion: Higher displacements and strains of bone tissue were observed below the RPD, especially in the region of the distal abutment and distal portion of the free‐end saddle. Strains within bone and the bone‐denture contact area were mostly influenced by the teeth and denture vertical displacement. 相似文献
The induction of chromosome aberrations in human lymphocytes irradiated in vitro with slow neutrons was examined to assess the maximum low-dose RBE (RBEM) relative to 60Co γ-rays. For the blood irradiations, cold neutron beam available at the prompt gamma activation analysis facility at the Munich research reactor FRM II was used. The given flux of cold neutrons can be converted into a thermally equivalent one. Since blood was taken from the same donor whose blood had been used for previous irradiation experiments using widely varying neutron energies, the greatest possible accuracy was available for such an estimation of the RBEM avoiding the inter-individual variations or differences in methodology usually associated with inter-laboratory comparisons. The magnitude of the coefficient α of the linear dose–response relationship (α = 0.400 ± 0.018 Gy?1) and the derived RBEM of 36.4 ± 13.3 obtained for the production of dicentrics by thermal neutrons confirm our earlier observations of a strong decrease in α and RBEM with decreasing neutron energy lower than 0.385 MeV (RBEM = 94.4 ± 38.9). The magnitude of the presently estimated RBEM of thermal neutrons is—with some restrictions—not significantly different to previously reported RBEM values of two laboratories. 相似文献
Sugar transport is very critical in developing an efficient and rapid conversion process of a mixture of sugars by engineered microorganisms. By using expressed sequence tag data generated for the fructophilic yeast Candida magnoliae JH110, we identified two fructose-specific transporters, CmFSY1 and CmFFZ1, which show high homology with known fructose transporters of other yeasts. The CmFSY1 and CmFFZ1 genes harbor no introns and encode proteins of 574 and 582 amino acids, respectively. Heterologous expression of the two fructose-specific transporter genes in a Saccharomyces cerevisiae, which is unable to utilize hexoses, revealed that both transporters are functionally expressed and specifically transport fructose. These results were further corroborated by kinetic analysis of the fructose transport that showed that CmFsy1p is a high-affinity fructose–proton symporter with low capacity (KM?=?0.13?±?0.01 mM, Vmax?=?2.1?±?0.3 mmol h?1 [gdw]?1) and that CmFfz1p is a low-affinity fructose-specific facilitator with high capacity (KM?=?105?±?12 mM, Vmax?=?8.6?±?0.7 mmol h?1 [gdw]?1). These fructose-specific transporters can be used for improving fructose transport in engineered microorganisms for the production of biofuels and chemicals from fructose-containing feedstock. 相似文献
The objectives of the present paper were: (i) to determine isotopically exchangeable zinc using two isotopic exchange methods (E and L values) in a series of polluted and non-polluted Swiss agricultural soils, and (ii) to evaluate the ability of chemical extraction methods to estimate plant-available soil Zn using isotopic techniques. The surface horizon (0–20 cm) of seven polluted and non-polluted soils representing a wide range in physico-chemical properties and Zn contents were sampled. An isotopic exchange kinetics (IEK) approach was used to assess, in a batch experiment, the isotopically exchangeable Zn content (E value). In order to determine the L values, a pot experiment was carried out with Lolium multiflorum (cv. Axis) in a growth chamber using a 65Zn-isotope dilution technique. Total Zn uptake and the isotopic composition (65Zn/stableZn) were determined in Lolium multiflorum for five successive cuts. The amounts of zinc extracted by different chemicals were compared with L values and regression parameters were estimated. The isotopic composition in soil extracted by DTPA and EDTAAc at the end of the pot experiment was also determined. Results showed that the equation describing the increase of isotopically exchangeable Zn with time could be extrapolated to three months for polluted and non-polluted neutral and acidic soils, and that the results were not different from the amount of isotopically exchangeable Zn experimentally determined with Lolium multiflorum (L value). In alkaline soils however, results suggest that either 65Zn sorption occurred in the batch experiment or that the concentration of Zn in the soil solution had been overestimated, leading to an overestimation of the E value compared to the L values. Furthermore, the specific activities measured in DTPA and EDTA extractions at the end of the pot experiment were significantly different compared to the specific activity of the plant, showing that both these chelating agents extract neither all the available soil Zn nor only the available soil Zn for plants. Abbreviations:CZn– concentration of Zn in a soil water extract (mg Zn L?1); CZn?Plant– concentration of Zn in plant shoots (mg Zn kg?1 DM); DTPA – diethylene triamine pentaacetic acid; E1\min– amount of Zn isotopically exchangeable within one min (mg Zn kg?1 soil); E(t)\exp– amount of Zn isotopically exchangeable after t min derived from experimental results (mg Zn kg?1 soil); E(t)pred– amount of Zn isotopically exchangeable after t min predicted using kinetic parameters derived from a 100 min long isotope exchange kinetic experiment together with CZn, and ZnHNO3 (mg Zn kg?1 soil); EDTA – ethylene diamine tetraacetic acid; ICP– isotopic composition of Zn in plant shoots; ICDTPA– isotopic composition of Zn in the soil DTPA extract; ICEDTA– isotopic composition of Zn in the soil EDTA extract; ICSE– isotopic composition of Zn in the soil extracts; IEK – isotope exchange kinetics; L value – amount of plant available Zn (mg Zn kg?1 soil); Lolium multiflorum; TEA – Triethanolamine; ZnDTPA– Zn extractable by 0.005 M DTPA + 0.01 M CaCl2 + 0.1 M TEA; ZnEDTA?NH4Ac– Zn extractable by 0.5 M NH4Ac, 0.02 M EDTA; ZnEDTA?Ca(NO3)2– Zn extractable by 0.005 M EDTA, 0.01 M Ca(NO3)2; ZnKCl– Zn extractable by 1 M KCl; ZnCaCl2– Zn extractable by 0.01 M CaCl2; ZnNaNO3– Zn extractable by 0.1 M NaNO3; ZnHNO3– Zn extractable by 2 M HNO3. 相似文献
A phosphodiesterase I (EC 3.1.4.1; PDE-I) was purified from Walterinnesia aegyptia venom by preparative native polyacrylamide gel electrophoresis (PAGE). A single protein band was observed in analytical native PAGE and sodium dodecyl sulfate (SDS)-PAGE. PDE-I was a single-chain glycoprotein with an estimated molecular mass of 158 kD (SDS-PAGE). The enzyme was free of 5′-nucleotidase and alkaline phosphatase activities. The optimum pH and temperature were 9.0 and 60°C, respectively. The energy of activation (Ea) was 96.4, the Vmax and Km were 1.14 µM/min/mg and 1.9 × 10?3M, respectively, and the Kcat and Ksp were 7 s?1 and 60 M?1 min?1 respectively. Cysteine was a noncompetitive inhibitor, with Ki = 6.2 × 10?3M and an IC50 of 2.6 mM, whereas adenosine diphosphate was a competitive inhibitor, with Ki = 0.8 × 10?3M and an IC50 of 8.3 mM. Glutathione, o-phenanthroline, zinc, and ethylenediamine tetraacetic acid (EDTA) inhibited PDE-I activity whereas Mg2+ slightly potentiated the activity. PDE-I hydrolyzed thymidine-5′-monophosphate p-nitrophenyl ester most readily, whereas cyclic 3′-5′-AMP was least susceptible to hydrolysis. PDE-I was not lethal to mice at a dose of 4.0 mg/kg, ip, but had an anticoagulant effect on human plasma. These findings indicate that W. aegyptia PDE-I shares various characteristics with this enzyme from other snake venoms. 相似文献
Monoaminergic dysregulation is implicated in attention-deficit/hyperactivity disorder (ADHD), and methylphenidate and amphetamines are the most frequently prescribed pharmacological agents for treating ADHD. However, it has recently been proposed that the core symptoms of the disorder might be due to an imbalance between monoaminergic and cholinergic systems. In this study, we used fibroblast cell homogenates from boys with and without ADHD as an extraneural cell model to examine the cholinergic receptor density, that is, muscarinic acetylcholine receptors (mAChRs). We found that the binding capacity (Bmax) of [3H] Quinuclidinyl benzilate (3H-QNB) to mAChRs was decreased by almost 50 % in the children with ADHD (mean = 30.6 fmol/mg protein, SD = 25.6) in comparison with controls [mean = 63.1 fmol/mg protein, SD = 20.5, p ≤ 0.01 (Student’s unpaired t test)]. The decreased Bmax indicates a reduced cholinergic receptor density, which might constitute a biomarker for ADHD. However, these preliminary findings need to be replicated in larger ADHD and comparison cohorts. 相似文献
To improve the thermostability of a mesophilic GH family 10 xylanase, AuXyn10A, from Aspergillus usamii E001, its modification was performed by in silico design. Based on the comparison of B-factor values, a mutant xylanase ATXyn10 was predicted by substituting a segment YP from Tyr25 to Pro34 of AuXyn10A with the corresponding one from Asn24 to Ala32 of TaXyn10, a thermophilic GH family 10 xylanase from Thermoascus aurantiacus. Analysis of a TaXyn10 crystal structure indicated that there is a close interaction between segments YP and FP. For that reason, another mutant xylanase ATXyn10M was designed by mutating Ser286 and His288 of ATXyn10 into the corresponding Gly285 and Phe287 in the FP of TaXyn10. Then, two ATXyn10- and ATXyn10M-encoding genes, ATxyn10 and ATxyn10M, were expressed in Pichia pastoris GS115. The temperature optimum of recombinant (re) ATXyn10M was 60 °C, 10 °C higher than that of reAuXyn10A. Its thermal inactivation half-life (t1/2) at 55 °C was 10.4-fold longer than that of reAuXyn10A. As compared with reAuXyn10A, reATXyn10M displayed a slight decrease in Km value and a significant increase in Vmax value from 6,267 to 8,870 U/mg. 相似文献
Proteins from the fresh roots of Stemona tuberosa (Stemonaceae) were extracted into 20 mM phosphate buffer, pH 7.2/0.1 M NaCl, precipitated with 90% saturation ammonium sulfate, and enriched by diethylaminoethanol (DEAE) cellulose. The protein eluted as a single main peak from the unbound fractions (ST-1), and appeared as a single band with superoxide dismutase (SOD) activity after native polyacrylamide gel electrophoresis (PAGE) resolution and zymogram development. ST-1 was classified as SOD due to its strong inhibition by HCN and H2O2. The amino acid sequence of three tryptic peptides of ST-1 matched with the SOD isozymes from Ananas comosus and Solanum lycopersicum. The SOD consisted of at least two heterologous protein subunits with molecular mass of 17.6 and 31.5 kD, respectively, and had an optimal SOD activity at pH 5 and over a temperature range of 0–50°C. MgCl2, MnCl2, and HgCl2 were strongly inhibitory at all concentrations tested. The SOD activity was completely negated in the presence of 0.5 mM SDS or 5 mM HgCl2. The relationship between riboflavin and nitroblue tetrazolium (NBT) on SOD activity was linear, giving Km and Vmax values of the purified SOD of 62.414 ± 0.015 M and 101.010 ± 0.022 µmol/min/mg protein for NBT and 27.389 ± 0.032 M and 38.167 ± 0.021 µmol/min/mg protein for riboflavin, respectively. 相似文献
This paper demonstrates Pseudomonas cepacia lipase catalyzed hydrolysis of p-nitrophenyl palmitate under irradiation of light with wavelengths of 250–750 nm. The reaction follows Michaelis–Menten Kinetics and the light irradiation increases the overall rate of hydrolysis. Using Lineweaver–Burk plot KM and Vmax values for the reaction in presence of light are found to be 39.07 and 66.67 mM/min/g, respectively; while for the same reaction under dark condition, the values are 7.08 and 10.21 mM/min/g. The linear form of enzyme dependent rate of reaction confirms that no mass-transfer limitations are present and the reaction is a kinetically controlled enzymatic reaction. 相似文献
The mechanisms for the acetylene hydrochlorination reaction on pristine Au7 and Au8 clusters and on the Si-doped Au clusters Au6Si and Au7Si were systematically investigated via density functional theory using the PBE functional. The band gap (?Eg) of the Au7Si cluster was found to smaller than that of its undoped equivalent (Au8), thus enhancing its catalytic activity, and Au7Si presented a significantly reduced activation barrier (16.69 kcal mol?1) for the acetylene hydrochlorination reaction compared with the pristine Au8 cluster (21.83 kcal mol?1). On the other hand, the activation barrier for the acetylene hydrochlorination reaction was not lower for the Au6Si cluster than for the pristine Au7 cluster because the band gap (?Eg) of Au6Si was found to be larger than that of Au7. Hence, the current work shows that the catalytic activities of gold clusters can be systematically modified by doping them. Our findings also suggest how to enhance the acetylene hydrochlorination reaction by doping foreign atoms into Au clusters.
Graphical abstract The Si-doped Au7Si cluster showed stronger catalytic activity for the acetylene hydrochlorination reaction compared with the pristine Au8 cluster.