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1.
It is commonly observed that the rate of enzymatic hydrolysis of solid cellulose substrates declines markedly with time. In
this work the mechanism behind the rate reduction was investigated using two dominant cellulases of Trichoderma reesei: exoglucanase Cel7A (formerly known as CBHI) and endoglucanase Cel7B (formerly EGI). Hydrolysis of steam-pretreated spruce
(SPS) was performed with Cel7A and Cel7B alone, and in reconstituted mixtures. Throughout the 48-h hydrolysis, soluble products,
hydrolysis rates, and enzyme adsorption to the substrate were measured. The hydrolysis rate for both enzymes decreases rapidly
with hydrolysis time. Both enzymes adsorbed rapidly to the substrate during hydrolysis. Cel7A and Cel7B cooperate synergistically,
and synergism was approximately constant during the SPS hydrolysis. Thermal instability of the enzymes and product inhibition
was not the main cause of reduced hydrolysis rates. Adding fresh substrate to substrate previously hydrolyzed for 24 h with
Cel7A slightly increased the hydrolysis of SPS; however, the rate increased even more by adding fresh Cel7A. This suggests
that enzymes become inactivated while adsorbed to the substrate and that unproductive binding is the main cause of hydrolysis
rate reduction. The strongest increase in hydrolysis rate was achieved by adding Cel7B. An improved model is proposed that
extends the standard endo-exo synergy model and explains the rapid decrease in hydrolysis rate. It appears that the processive
action of Cel7A becomes hindered by obstacles in the lignocellulose substrate. Obstacles created by disordered cellulose chains
can be removed by the endo activity of Cel7B, which explains some of the observed synergism between Cel7A and Cel7B. The improved
model is supported by adsorption studies during hydrolysis. 相似文献
2.
Ersuo Jin Yu Zhang Fanghui Hu Fang Yang Shufang Wu Yongcan Jin Junlong Song 《Cellulose (London, England)》2017,24(3):1371-1381
The role of the cellulose ultrastructure on the relationship between cellulase binding and activity is not clear yet. In this article, a quartz crystal microbalance with dissipation (QCM-D) was employed to monitor the interactions between a given cellulase and the cellulose substrates with varied polymorphs of pure cellulose I and II and the intermediate state (I/II). Initially, cellulose nanocrystals (CNCs) with polymorphs of cellulose I, I/II and II were prepared and spin-coated on QCM sensors. The cellulose substrates’ crystallinity degree was examined by XRD, and morphology was detected by AFM. Then, a commercial cellulase from Trichoderma reesei was used to test the adsorption and hydrolysis of cellulose substrates with polymorphs of I, I/II and II, respectively. The results revealed that in the enzyme adsorption and desorption process at a temperature of 15 °C, CNC-II had the lowest adsorption capacity with a total adsorption mass of 179 ng cm?2 but the highest reversible binding ratio of 33.7%; for comparison, the values were 235 ng cm?2 versus 25.6% and 207 ng cm?2 versus 26.9% for CNC-I and -I/II, respectively. And the conformation of adlayers on CNC-I, -I/II and -II derived from the QCM data became softer and softer in turn. On the other hand, CNC-II exhibited the best enzymatic hydrolytic ability among three substrates when enzymatic hydrolysis experiments were conducted at 45 °C. The results indicated that polymorphic conversion from I to II changes the affinity between the enzyme and cellulose surface; CNC-II has the lowest affinity to the enzyme, but the softer conformation of the adsorbed enzyme layer, and the more reversible adsorption may facilitate its hydrolytic activity. This article gives a perspective from the adsorption dynamics and conformation of the adsorbed enzyme layer, helping to understand the superior hydrolytic activity of cellulose with polymorph II. Thus, there is a potential of polymorphic conversion in the reduction of enzyme dosage and cost in the enzymatic hydrolysis process. 相似文献
3.
The mechanism of hydrolysis of cellulose is important for improving the enzymatic conversion in bioprocesses based on lignocellulose. Adsorption and hydrolysis experiments were performed with cellobiohydrolase I (CBH I) and endoglucanase II (EG II) from Trichoderma reesei on a realistic lignocellulose substrates: steam-pretreated willow. The enzymes were studied both alone and in equimolar mixtures. Adsorption isotherms were determined at 4 and 40 degrees C during 90-min reaction times. Both CBH I and EG II adsorbed stronger at 40 than at 4 degrees C. The time course of adsorption and hydrolysis, 3 min to 48 h, was studied at 40 degrees C. About 90% of the cellulases were adsorbed within 2 h. The hydrolysis rate was high in the beginning but decreased during the time course. Based on adsorption data, the hydrolysis and synergism were analyzed as function of adsorbed enzyme. CBH I showed a linear correlation between hydrolysis and adsorbed enzyme, whereas for EG II the corresponding curve leveled off at both 4 and 40 degrees C. At low conversion, below 1%, EG II produced as much soluble sugars as CBH I. At higher conversion, CBH I was more efficient than EG II. The synergism as function of adsorbed enzyme increased with bound enzyme before reaching a stable value of about 2. The effect of varying the ratio of CBH I:EG II was studied at fixed total enzyme loading and by changing the ratio between the enzymes. Only a small addition (5%) of EG II to a CBH I solution was shown to be sufficient for nearly maximal synergism. The ratio between EG II and CBH I was not critical. The ratio 40% EG II:60% CBH I showed similar conversion to 5% EG II:95% CBH I. Modifications of the conventional endo-exo synergism model are proposed. 相似文献
4.
Enhancing the enzymatic hydrolysis of cellulosic materials using simultaneous ball milling 总被引:1,自引:0,他引:1
Mais Ursula Esteghlalian Ali R. Saddler John N. Mansfield Shawn D. 《Applied biochemistry and biotechnology》2002,98(1-9):815-832
One of the limiting factors restricting the effective and efficient bioconversion of softwood-derived lignocellulosic residues
is the recalcitrance of the substrate following pretreatment. Consequently, the ensuing enzymatic process requires relatively
high enzyme loadings to produce monomeric carbohydrates that are readily fermentable by ethanologenic microorganisms. In an
attempt to circumvent the need for larger enzyme loadings, a simultaneous physical and enzymatic hydrolysis treatment was
evaluated. A ball-mill reactor was used as the digestion vessel, and the extent and rate of hydrolysis were monitored. Concurrently,
enzyme adsorption profiles and the rate of conversion during the course of hydrolysis were monitored. α-Cellulose, employed
as a model substrate, and SO2-impregnated steam-exploded Douglas-fir wood chips were assessed as the cellulosic substrates. The softwood-derived substrate
was further posttreated with water and hot alkaline hydrogen peroxide to remove >90% of the original lignin. Experiments at
different reaction conditions were evaluated, including substrate concentration, enzyme loading, reaction volumes, and number
of ball beads employed during mechanical milling. It was apparent that the best conditions for the enzymatic hydrolysis of
α-cellulose were attained using a higher number of beads, while the presence of air-liquid interface did not seem to affect
the rate of saccharification. Similarly, when employing the lignocellulosic substrate, up to 100% hydrolysis could be achieved
with a minimum enzyme loading (10 filter paper units/g of cellulose), at lower substrate concentrations and with a greater
number of reaction beads during milling. It was apparent that the combined strategy of simultaneous ball milling and enzymatic
hydrolysis could improve the rate of saccharification and/or reduce the enzyme loading required to attain total hydrolysis
of the carbohydrate moieties. 相似文献
5.
Johan P. Olsen Bryon S. Donohoe Kim Borch Peter Westh Michael G. Resch 《Cellulose (London, England)》2016,23(4):2349-2361
It is well documented that the enzymatic hydrolysis of cellulose follows a reaction pattern where an initial phase of relatively high activity is followed by a gradual slow-down over the entire course of the reaction. This phenomenon is not readily explained by conventional factors like substrate depletion, product inhibition or enzyme instability. It has been suggested that the underlying reason for the loss of enzyme activity is connected to the heterogeneous structure of cellulose, but so far attempts to establish quantitative measures of such a correlation remain speculative. Here, we have carried out an extensive microscopy study of Avicel particles during extended hydrolysis with Hypocrea jecorina cellobiohydrolase 1 (CBH1) and endoglucanase 1 and 3 (EG1 and EG3) alone and in mixtures. We have used differential interference contrast microscopy and transmission electron microscopy to observe and quantify structural features at μm and nm resolution, respectively. We implemented a semi-automatic image analysis protocol, which allowed us to analyze almost 3000 individual micrographs comprising a total of more than 300,000 particles. From this analysis we estimated the temporal development of the accessible surface area throughout the reaction. We found that the number of particles and their size as well as the surface roughness contributed to surface area, and that within the investigated degree of conversion (<30 %) this measure correlated linearly with the rate of reaction. Based on this observation we argue that cellulose structure, specifically surface area and roughness, plays a major role in the ubiquitous rate loss observed for cellulases. 相似文献
6.
A new type of reactor, the attrition bioreactor, has been developed to increase the rate of the enzymatic hydrolysis of cellulose
and also to cut pretreatment costs. It was found that the attrition bioreactor could be operated continuously or semicontinuously
in conjunction with a membrane filter to produce a high cellulose conversion rate and low enzyme consumption. The membrane
filter served to contain the enzyme and cellulose within the reactor while allowing sugar to permeate as a product. 相似文献
7.
Pavle Andri? Anne S. Meyer Peter A. Jensen Kim Dam-Johansen 《Applied biochemistry and biotechnology》2010,160(1):280-297
The enzymatic hydrolysis of lignocellulosic biomass is known to be product-inhibited by glucose. In this study, the effects
on cellulolytic glucose yields of glucose inhibition and in situ glucose removal were examined and modeled during extended
treatment of heat-pretreated wheat straw with the cellulolytic enzyme system, Celluclast? 1.5 L, from Trichoderma reesei, supplemented with a β-glucosidase, Novozym? 188, from Aspergillus niger. Addition of glucose (0–40 g/L) significantly decreased the enzyme-catalyzed glucose formation rates and final glucose yields,
in a dose-dependent manner, during 96 h of reaction. When glucose was removed by dialysis during the enzymatic hydrolysis,
the cellulose conversion rates and glucose yields increased. In fact, with dialytic in situ glucose removal, the rate of enzyme-catalyzed
glucose release during 48–72 h of reaction recovered from 20–40% to become ≈70% of the rate recorded during 6–24 h of reaction.
Although Michaelis–Menten kinetics do not suffice to model the kinetics of the complex multi-enzymatic degradation of cellulose,
the data for the glucose inhibition were surprisingly well described by simple Michaelis–Menten inhibition models without
great significance of the inhibition mechanism. Moreover, the experimental in situ removal of glucose could be simulated by
a Michaelis–Menten inhibition model. The data provide an important base for design of novel reactors and operating regimes
which include continuous product removal during enzymatic hydrolysis of lignocellulose. 相似文献
8.
Esteghlalian Ali R. Srivastava Vinit Gilkes Neil R. Kilburn Douglas G. Warren R. Antony J. Saddler John N. 《Applied biochemistry and biotechnology》2001,91(1-9):575-592
This article provides an overview of various theories proposed during the past five decades to describe the enzymatic hydrolysis
of cellulose highlighting the major shifts that these theories have undergone. It also describes the effect of the cellulose-binding
domain (CBD) of an exoglucanase/xylanase from bacterium Cellulomonas fimi on the enzymatic hydrolysis of Avicel. Pretreatment of Avicel with CBDCex at 4 and 37°C as well as simultaneous addition of CBDCex to the hydrolytic enzyme (Celluclast, Novo, Nordisk) reduced the initial rate of hydrolysis owing to irreversible binding
of CBD proteins to the substrate's binding sites. Nonetheless, near complete hydrolysis was achieved even in the presence
of CBDCex. Protease treatment of both pure and CBDCex-treated Avicel reduced the substrates' hydrolyzability, perhapsowing to proteolysis of the hydrolyzing enzyme (Celluclast)
by the residual Proteinase K remaining in the substrate. Better protocols for comptete removal of CBD proteins from the substrate
need to be developed to investigate the effect of CBD adsorption on cellulose digestibility. 相似文献
9.
In this work, we examined the role of a non-ionic surfactant, Tween 20, on enzymatic hydrolysis of lignocelluloses. Delignified
lignocelluloses (pine wood chip) were used as model substrates. Effects of Tween 20 on adsorption/desorption onto/from lignocelluloses
with and without hydrolysis were evaluated respectively. Tween 20 lowered the non-biospecific adsorption of β-glucosidase and enhanced the bio-specific adsorption of cellulase. Tween 20 did not affect the liquid phase reaction (cellobiose
hydrolysis). However, for the solid surface reaction (cellulose hydrolysis), cellulose conversion for 72 hrs was increased
9–21% and 1–8.5% for samples with high lignin contents (PI) and low lignin contents (PIII) by injection of Tween 20 (0.024–0.24 mM),
respectively. Moreover, Tween 20 increased the cellulose conversion rate substantially. It is suggested that the increase
of cellulase amount adsorbed due to the increase of effective cellulose surface by Tween 20 contribute to the enhancement
of cellulose conversion. 相似文献
10.
We present a new assay based on total internal reflection fluorescence (TIRF) to quantify the catalytic activity of adsorbed enzyme monolayers on macroscopically flat surfaces. The need for such an assay derives from a general shortage of assay methods that are sufficiently sensitive to measure reaction kinetics for just a single monolayer of enzymes. The assay is based on the enzymatic conversion of a soluble, nonfluorescent fluorogenic substrate reagent to a soluble, highly fluorescent product. The reaction occurs at the solid-liquid interface where the enzymes are adsorbed. Fluorogenic substrates are introduced to the adsorbed layer by convective diffusion from solutions undergoing steady laminar slit flow. The exponentially decaying evanescent wave that is produced by total internal reflection serves as a "spectroscopic ruler" to resolve the spatial concentration profile of fluorescent products in solution near the interface. By measuring the steady-state fluorescence signal as a function of the Peclet number that characterizes mass transfer conditions in the experiment, it is possible to determine the enzymatic reaction rate. Here we present the development of the method and its application to a test system of beta-galactosidase adsorbed to methylated silica surfaces. Compared to the enzymatic rate constants for this enzyme in free solution, adsorption decreased the Michaelis-Menten rate constant kcat by a factor of 10 and increased the equilibrium binding constant Km by a factor of 4.5. Thus the intrinsic activity of the enzyme, as represented by the ratio kcat/Km, decreased 45-fold due to adsorption. Copyright 1999 Academic Press. 相似文献
11.
Wei Liao Zhiyou Wen Sharon Hurley Yan Liu Chuanbin Liu Shulin Chen 《Applied biochemistry and biotechnology》2005,124(1-3):1017-1030
This study focused on the effect of hemicellulose and lignin on enzymatic hydrolysis of dairy manure and hydrolysis process
optimization to improve sugar yield. It was found that hemicellulose and lignin in dairy manure, similar to their role in
other lignocellulosic material, were major resistive factors to enzymatic hydrolysis and that the removal of either of them,
or for best performance, both of them, improved the enzymatic hydrolysis of manure cellulose. This result combined with scanning
electron microscope (SEM) pictures further proved that the accessibility of cellulose to cellulase was the most important
feature to the hydrolysis. Quantitatively, fed-batch enzymatic hydrolysis of fiber without lignin and hemicellulose had a
high glucose yield of 52% with respect to the glucose concentration of 17 g/L at a total enzyme loading of 1300 FPU/L and
reaction time of 160 h, which was better than corresponding batch enzymatic hydrolysis. 相似文献
12.
Benjamin T. Smith Jeffrey S. Knutsen Robert H. Davis 《Applied biochemistry and biotechnology》2010,161(1-8):468-482
The cellulose hydrolysis kinetics during batch enzymatic saccharification are typified by a rapid initial rate that subsequently decays, resulting in incomplete conversion. Previous studies suggest that changes associated with the solution, substrate, or enzymes may be responsible. In this work, kinetic experiments were conducted to determine the relative magnitude of these effects. Pretreated corn stover (PCS) was used as a lignocellulosic substrate likely to be found in a commercial saccharification process, while Avicel and Kraft lignin were used to create model substrates. Glucose inhibition was observed by spiking the reaction slurry with glucose during initial-rate experiments. Increasing the glucose concentration from 7 to 48 g/L reduced the cellulose conversion rate by 94%. When product sugars were removed using ultrafiltration with a 10 kDa membrane, the glucose-based conversion increased by 9.5%. Reductions in substrate reactivity with conversion were compared directly by saccharifying PCS and Avicel substrates that had been pre-reacted to different conversions. Reaction of substrate with a pre-conversion of 40% resulted in about 40% reduction in the initial rate of saccharification, relative to fresh substrate with identical cellulose concentration. Overall, glucose inhibition and reduced substrate reactivity appear to be dominant factors, whereas minimal reductions of enzyme activity were observed. 相似文献
13.
The effect of two types of cellulose, microcrystalline cellulose and paper pulp, on enzymatic hydrolysis for cellobiose production
was investigated. The particle size, the relative crystallinity index and the water retention value were determined for both
celluloses. A previously studied multistage hydrolysis process that proved to enhance the cellobiose production was studied
with both types of celluloses. The cellobiose yield exhibited a significant improvement (120% for the microcrystalline cellulose
and 75% for the paper pulp) with the multistage hydrolysis process compared to continuous hydrolysis. The conversion of cellulose
to cellobiose was greater for the microcrystalline cellulose than for the paper pulp. Even with high crystallinity, microcrystalline
cellulose achieved the highest cellobiose yield probably due to its highest specific surface area accessible to enzymes and
quantity of adsorbed protein. 相似文献
14.
Masahiro Kurakake Takeshi Shirasawa Hiroshi Ooshima Alvin O. Converse Jyoji Kato 《Applied biochemistry and biotechnology》1995,50(3):231-241
Three empirical rate expressions, Kinetics I, II, and III, for the enzymatic hydrolysis of cellulose were evaluated in an
effort to develop a easy-to-use rate expression. They are based on the following equation:-dV/dX = kV, where V and X are the hydrolysis rate and the fractional conversion. In Kinetic I,k is constant. In Kinetic II, a linear relatinship betweenk and t is assumed. In Kinetic III, an exponential relationship is assumed. The three expressions were applied to enzymatic
hydrolysis carried out under seven different conditions in which the kinds of substrates, enzymes, and initial concentrations
were varied. All of the examined rate expressions were applied to the hydrolysis with success, but the better accuracies were
obtained by Kinetic III, Kinetic II, and Kinetic I in this order. The variations ofk with time found in this study, especially the exponential relationship, were consistent with the effect of the measured changes
in the concentration of adsorbed enzyme as predicted by theory developed previously by Ooshima et al. (1). 相似文献
15.
Diana Ciolacu Selestina Gorgieva Daniel Tampu Vanja Kokol 《Cellulose (London, England)》2011,18(6):1527-1541
This paper investigates the enzymatic hydrolysis of three main allomorphic forms of microcrystalline cellulose using different
cellulases, from Trichoderma reesei and from Aspergillus niger, respectively. It was demonstrated that both the morphological and crystalline structures are important parameters that have
a great influence on the course of the hydrolysis process. The efficiency of the enzymatic hydrolysis of cellulosic substrates
was estimated by the amounts of reducing sugar and by the yield of the reaction. Changes in the average particle sizes of
the cellulose allomorphs were determined during enzymatic hydrolysis. The accumulation of soluble sugar within the supernatant
was used as a measure of the biodegradation process’s efficiency, and was established by HPLC-SEC analysis. Any modifications
in the supramolecular structure of the cellulosic residues resulting from the enzymatic hydrolysis were determined by X-ray
diffraction. The action of each cellulase was demonstrated by a reduction in the crystalline index and the crystallite dimensions
of the corresponding allomorphic forms. The crystalline structure of allomorphic forms I and II did not suffer significant
modifications, while cellulose III recorded a partial return to the crystalline structure of cellulose I. The microstructures
of cellulose allomorph residues were presented using optical microscopy and scanning electron microscopy. 相似文献
16.
Zheng Y Pan Z Zhang R Wang D Jenkins B 《Applied biochemistry and biotechnology》2008,146(1-3):231-248
Our previous research has shown that saline Creeping Wild Ryegrass (CWR), Leymus triticoides, has a great potential to be used for bioethanol production because of its high fermentable sugar yield, up to 85% cellulose
conversion of pretreated CWR. However, the high cost of enzyme is still one of the obstacles making large-scale lignocellulosic
bioethanol production economically difficult. It is desirable to use reduced enzyme loading to produce fermentable sugars
with high yield and low cost. To reduce the enzyme loading, the effect of addition of non-ionic surfactants and non-catalytic
protein on the enzymatic hydrolysis of pretreated CWR was investigated in this study. Tween 20, Tween 80, and bovine serum
albumin (BSA) were used as additives to improve the enzymatic hydrolysis of dilute sulfuric-acid-pretreated CWR. Under the
loading of 0.1 g additives/g dry solid, Tween 20 was the most effective additive, followed by Tween 80 and BSA. With the addition
of Tween 20 mixed with cellulase loading of 15 FPU/g cellulose, the cellulose conversion increased 14% (from 75 to 89%), which
was similar to that with cellulase loading of 30 FPU/g cellulose and without additive addition. The results of cellulase and
BSA adsorption on the Avicel PH101, pretreated CWR, and lignaceous residue of pretreated CWR support the theory that the primary
mechanism behind the additives is prevention of non-productive adsorption of enzymes on lignaceous material of pretreated
CWR. The addition of additives could be a promising technology to improve the enzymatic hydrolysis by reducing the enzyme
activity loss caused by non-productive adsorption. 相似文献
17.
Rosgaard L Andric P Dam-Johansen K Pedersen S Meyer AS 《Applied biochemistry and biotechnology》2007,143(1):27-40
In this study, the applicability of a “fed-batch” strategy, that is, sequential loading of substrate or substrate plus enzymes
during enzymatic hydrolysis was evaluated for hydrolysis of steam-pretreated barley straw. The specific aims were to achieve
hydrolysis of high substrate levels, low viscosity during hydrolysis, and high glucose concentrations. An enzyme system comprising
Celluclast and Novozyme 188, a commercial cellulase product derived from Trichoderma reesei and a β-glucosidase derived from Aspergillus niger, respectively, was used for the enzymatic hydrolysis. The highest final glucose concentration, 78 g/l, after 72 h of reaction,
was obtained with an initial, full substrate loading of 15% dry matter weight/weight (w/w DM). Conversely, the glucose yields,
in grams per gram of DM, were highest at lower substrate concentrations, with the highest glucose yield being 0.53 g/g DM
for the reaction with a substrate loading of 5% w/w DM after 72 h. The reactions subjected to gradual loading of substrate
or substrate plus enzymes to increase the substrate levels from 5 to 15% w/w DM, consistently provided lower concentrations
of glucose after 72 h of reaction; however, the initial rates of conversion varied in the different reactions. Rapid cellulose
degradation was accompanied by rapid decreases in viscosity before addition of extra substrate, but when extra substrate or
substrate plus enzymes were added, the viscosities of the slurries increased and the hydrolytic efficiencies decreased temporarily. 相似文献
18.
Thomas Stauner Igor B. Silva Omar A. El Seoud Elisabete Frollini Denise F. S. Petri 《Cellulose (London, England)》2013,20(3):1109-1119
The enzymatic hydrolysis of cotton raw cellulose (RC) samples, sieved RC samples through meshes <100 (CS1), 100–200 (C12), 200–400 (C24), mercerized RC samples (M-C), freeze-dried RC (RC-FD) samples, microcrystalline cellulose Avicel, bacterial cellulose (BC), raw sisal pulp and mercerized sisal pulp (S-M) was performed at cellulose-to-cellulase mass ratios of 1,000:1, 699:1, 400:1, 100:1 and 10:1. The index of crystallinity and water sorption values were quantified for all samples. The morphological features were analyzed by means of scanning electron microscopy (SEM). For cellulose-to-cellulase mass ratio of 100:1 and 10:1, the maximum hydrolysis extents of cellulose samples after 24 h reaction could not be correlated with their physical characteristics. However, hydrolyses of samples with large water sorption values were faster than those with lower water sorption values. The hydrolysis efficiency decreased when the cellulose-to-cellulase mass ratio was greater than 400:1; under this condition a remarkable dependence of the hydrolysis yield on the type of cellulosic sample was observed. The water sorption ability could be directly correlated with the hydrolysis extent, except for RC-FD and BC samples, which presented the lowest values. In the former, freeze-drying has led to pore collapse, with concomitant reduction of the amount of adsorbed water. For the latter sample, the densely packed structure made the water sorption slower than in all other samples. Despite of this fact, the presence of nanofibrils on the surface of BC (as detected by SEM) improved the enzyme adsorption, indicating that analysis by complementary techniques should be performed in order to predict the enzymatic hydrolysis efficiency. 相似文献
19.
A. B. Maidina A. B. Belova A. V. Levashov N. L. Klyachko 《Moscow University Chemistry Bulletin》2008,63(2):108-110
This work studies safflower oil hydrolysis catalyzed by Candida rugosa lipase as a function of temperature in an oil-in-water emulsion stabilized by the surfactant sodium deoxycholate. The choice of temperature for this reaction is dictated by the effects of temperature not only on the catalytic activity and stability of the enzyme but also on the state of the reaction medium (emulsion), whose quality substantially affects both the kinetic parameters of lipase and the product (linoleic acid) yield. For example, although the highest initial rate of the enzymatic reaction is observed at 40°C and the enzyme is virtually not inactivated during incubation (45°C), the highest reaction yield is observed at 30°C and decreases upon temperature elevation because of a change in the emulsion quality. 相似文献
20.
Weak‐Acid Sites Catalyze the Hydrolysis of Crystalline Cellulose to Glucose in Water: Importance of Post‐Synthetic Functionalization of the Carbon Surface 下载免费PDF全文
Dr. Anh The To Dr. Po‐Wen Chung Prof. Dr. Alexander Katz 《Angewandte Chemie (International ed. in English)》2015,54(38):11050-11053
The direct hydrolysis of crystalline cellulose to glucose in water without prior pretreatment enables the transformation of biomass into fuels and chemicals. To understand which features of a solid catalyst are most important for this transformation, the nanoporous carbon material MSC‐30 was post‐synthetically functionalized by oxidation. The most active catalyst depolymerized crystalline cellulose without prior pretreatment in water, providing glucose in an unprecedented 70 % yield. In comparison, virtually no reaction was observed with MSC‐30, even when the reaction was conducted in aqueous solution at pH 2. As no direct correlations between the activity of this solid–solid reaction and internal‐site characteristics, such as the β‐glu adsorption capacity and the rate of catalytic hydrolysis of adsorbed β‐glu strands, were observed, contacts of the external surface with the cellulose crystal are thought to be key for the overall efficiency. 相似文献