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Cellulose Hydrolysis (cellulose + hydrolysis)
Selected AbstractsEffect of Cellulase Mole Fraction and Cellulose Recalcitrance on Synergism in Cellulose Hydrolysis and BindingBIOTECHNOLOGY PROGRESS, Issue 1 2006Tina Jeoh Elucidating the molecular mechanisms that govern synergism is important for the rational engineering of cellulase mixtures. Our goal was to observe how varying the loading molar ratio of cellulases in a binary mixture and the recalcitrance of the cellulose to enzymatic degradation influenced the degree of synergistic effect (DSE) and degree of synergistic binding (DSB). The effect of cellulose recalcitrance was studied using a bacterial microcrystalline cellulose (BMCC), which was exhaustively hydrolyzed by a catalytic domain of Cel5A, an endocellulase. The remaining prehydrolyzed BMCC (PHBMCC) was used to represent a recalcitrant form of cellulose. DSE was observed to be sensitive to loading molar ratio. However, on the more recalcitrant cellulose, synergism decreased. Furthermore, the results from this study reveal that when an exocellulase (Cel6B) is mixed with either an endocellulase (Cel5A) or a processive endocellulase (Cel9A) and reacted with BMCC, synergism is observed in both hydrolysis and binding. This study also revealed that when a "classical" endocellulase (Cel5A) and a processive endocellulase (Cel9A) are mixed and reacted with BMCC, only limited synergism is observed in reducing sugar production; however, binding is clearly increased by the presence of the Cel5A. [source] Characterization of Dicarboxylic Acids for Cellulose HydrolysisBIOTECHNOLOGY PROGRESS, Issue 3 2001Nathan S. Mosier In this paper, we show that dilute maleic acid, a dicarboxylic acid, hydrolyzes cellobiose, the repeat unit of cellulose, and the microcrystalline cellulose Avicel as effectively as dilute sulfuric acid but with minimal glucose degradation. Maleic acid, superior to other carboxylic acids reported in this paper, gives higher yields of glucose that is more easily fermented as a result of lower concentrations of degradation products. These results are especially significant because maleic acid, in the form of maleic anhydride, is widely available and produced in large quantities annually. [source] Cellulose hydrolysis in evolving substrate morphologies III: Time-scale analysisBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2010Wen Zhou Abstract We present a time-scale analysis for the enzymatic hydrolysis of solid cellulosic substrates, based on our recently developed kinetic model (Zhou et al., 2009a, Biotechnol Bioeng 104:261,274; Zhou et al., 2009b, Biotechnol Bioeng 104:275,289) which incorporates both enzymatic chain fragmentation and hydrolytic time evolution of the solid substrate morphology. Analytical order-of-magnitude estimates of the relevant single-layer chain depolymerization times are first discussed. These time-scale estimates for pure and mixed enzyme systems can be employed to calculate the degree of synergy between endo - and exo -acting enzymes in a mixed enzyme system. By the way of a quasi-steady-state approximation which allows for a greatly simplified analytical solution of the model, we also explain the origin and give order-of-magnitude estimates of the two characteristic hydrolysis time scales which arise in this model when the solid substrate morphology is taken into account. These analytically derived time-scale relations explain how the embedding of cellulose chains in a solid substrate acts as a crucial rate-limiting factor and results in a substantial slowing down of the hydrolytic conversion process, compared to a hypothetical substrate of immediately enzyme-accessible, isolated chains. The analytical time-scale results are verified by numerical simulations and compared to experimental observations. Biotechnol. Bioeng. 2010;107: 224,234. © 2010 Wiley Periodicals, Inc. [source] Mechanism of substrate inhibition in cellulose synergistic degradationFEBS JOURNAL, Issue 16 2001Priit Väljamäe ,A comprehensive experimental study of substrate inhibition in cellulose hydrolysis based on a well defined system is presented. The hydrolysis of bacterial cellulose by synergistically operating binary mixtures of cellobiohydrolase I from Trichoderma reesei and five different endoglucanases as well as their catalytic domains displays a characteristic substrate inhibition. This inhibition phenomenon is shown to require the two-domain structure of an intact cellobiohydrolase. The experimental data were in accordance with a mechanism where cellobiohydrolases previously bound to the cellulose by means of their cellulose binding domains are able to find chain ends by lateral diffusion. An increased substrate concentration at a fixed enzyme load will also increase the average diffusion distance/time needed for cellobiohydrolases to reach new chain ends created by endoglucanases, resulting in an apparent substrate inhibition of the synergistic action. The connection between the binding properties and the substrate inhibition is encouraging with respect to molecular engineering of the binding domain for optimal performance in biotechnological processes. [source] Binding modules alter the activity of chimeric cellulases: Effects of biomass pretreatment and enzyme source,BIOTECHNOLOGY & BIOENGINEERING, Issue 4 2010Tae-Wan Kim Abstract Improving the catalytic activity of cellulases requires screening variants against solid substrates. Expressing cellulases in microbial hosts is time-consuming, can be cellulase specific, and often leads to inactive forms and/or low yields. These limitations have been obstacles for improving cellulases in a high-throughput manner. We have developed a cell-free expression system and used it to express 54 chimeric bacterial and archaeal endoglucanases (EGs), with and without cellulose binding modules (CBMs) at either the N- or C-terminus, in active enzyme yields of 100,350,µg/mL. The platform was employed to systematically study the role of CBMs in cellulose hydrolysis toward a variety of natural and pretreated solid substrates, including ionic-liquid pretreated Miscanthus and AFEX-pretreated corn stover. Adding a CBM generally increased activity against crystalline Avicel, whereas for pretreated substrates the effect of CBM addition depended on the source of cellulase. The cell-free expression platform can thus provide insights into cellulase structure-function relationships for any substrate, and constitutes a powerful discovery tool for evaluating or engineering cellulolytic enzymes for biofuels production. Biotechnol. Bioeng. 2010;107:601,611. © 2010 Wiley Periodicals, Inc. [source] A mechanistic model of the enzymatic hydrolysis of celluloseBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2010Seth E. Levine Abstract A detailed mechanistic model of enzymatic cellulose hydrolysis has been developed. The behavior of individual cellulase enzymes and parameters describing the cellulose surface properties are included. Results obtained for individual enzymes (T. reesei endoglucanase 2 and cellobiohydrolase I) and systems with both enzymes present are compared with experimental literature data. The model was sensitive to cellulase-accessible surface area; the EG2,CBHI synergy observed experimentally was only predicted at a sufficiently high cellulose surface area. Enzyme crowding, which is more apparent at low surface areas, resulted in differences between predicted and experimental rates of hydrolysis. Model predictions also indicated that the observed decrease in hydrolysis rates following the initial rate of rapid hydrolysis is not solely caused by product inhibition and/or thermal deactivation. Surface heterogeneities, which are not accounted for in this work, may play a role in decreasing the hydrolysis rate. The importance of separating the enzyme adsorption and complexation steps is illustrated by the model's sensitivity to the rate of formation of enzyme,substrate complexes on the cellulose surface. Biotechnol. Bioeng. 2010;107: 37,51. © 2010 Wiley Periodicals, Inc. [source] Optimization of enzyme complexes for lignocellulose hydrolysisBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2007Alex Berlin Abstract The ability of a commercial Trichoderma reesei cellulase preparation (Celluclast 1.5L), to hydrolyze the cellulose and xylan components of pretreated corn stover (PCS) was significantly improved by supplementation with three types of crude commercial enzyme preparations nominally enriched in xylanase, pectinase, and ,-glucosidase activity. Although the well-documented relief of product inhibition by ,-glucosidase contributed to the observed improvement in cellulase performance, significant benefits could also be attributed to enzymes components that hydrolyze non-cellulosic polysaccharides. It is suggested that so-called "accessory" enzymes such as xylanase and pectinase stimulate cellulose hydrolysis by removing non-cellulosic polysaccharides that coat cellulose fibers. A high-throughput microassay, in combination with response surface methodology, enabled production of an optimally supplemented enzyme mixture. This mixture allowed for a ,twofold reduction in the total protein required to reach glucan to glucose and xylan to xylose hydrolysis targets (99% and 88% conversion, respectively), thereby validating this approach towards enzyme improvement and process cost reduction for lignocellulose hydrolysis. Biotechnol. Bioeng. 2007;97: 287,296. © 2006 Wiley Periodicals, Inc. [source] Synergistic cellulose hydrolysis can be described in terms of fractal-like kineticsBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2003Priit Väljamäe Abstract A fractal-like kinetics model was used to describe the synergistic hydrolysis of bacterial cellulose by Trichoderma reesei cellulases. The synergistic action of intact cellobiohydrolase Cel7A and endoglucanase Cel5A at low enzyme-to-substrate ratios showed an apparent substrate inhibition consistent with a case where two-dimensional (2-D) surface diffusion of the cellobiohydrolase is rate-limiting. The action of Cel7A core and Cel5A was instead consistent with a three-dimensional (3-D) diffusion-based mode of action. The synergistic action of intact Cel7A was far superior to that of the core at a high enzyme-to-substrate ratio, but this effect was gradually reduced at lower enzyme-to-substrate ratios. The apparent fractal kinetics exponent h obtained by nonlinear fit of hydrolysis data to the fractal-like kinetics analogue of a first-order reaction was a useful empirical parameter for assessing the rate retardation and its dependence on the reaction conditions. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 84: 254,257, 2003. [source] |