Cellulose cellulase enzyme action

Cellulase enzyme complexes consist of three major types of proteins that synergistically catalyze the breakdown of a cellulosic substrate. Because the enzymes are strictly substrate-specific in their action, any change in the structure or accessibility of the substrate can have a considerable influence on the course of the hydrolysis reaction. A pretreatment method based on exposing cellulosic substrate to phosphoric acid solution [9] and addition of the nonionic... 

This session deals with recent progress on pretreatment of lignocellu-losic biomass, the peripheral reactions associated with pretreatment, and assessment of the effectiveness of pretreatment by enzymatic hydrolysis. Pretreatment is an essential element of the integral bioconversion process, and its objective is to enhance the susceptibility of cellulosic substrates to the action of cellulase enzymes. 

Irrespective of the type of biomass used for ethanol production, the biomass needs to be pretreated to make the carbohydrates available for fermentation. However, which enzymes can be used depends on the source of the biomass. In addition, the biomass needs pretreatment before the enzymes are used. The first step of the pretreatment can be of a physical nature. Once the biomass is physically pretreated, the cellulose structures are open for enzyme action. In biomass from forests, the substance is mainly in the form of cellulose. Targeted enzymes are selective for the reaction of cellulose to glucose, and therefore there are no degradation byproducts, as occurs in acid conversion technology. There are at least three ways this can be performed. Firstly, in separate hydrolysis and fermentation, the pretreated biomass is treated with cellulase, which hydrolyzes the cellulose to glucose at 50 °C and pH 4.8. Secondly, in simultaneous fermentation and saccharification (SSF) the hydrolysis and fermentation take place in the same bioreactor. Thirdly,... 

When cellulase acts on cellulose, the most susceptible portions are rapidly digested, and the residue becomes increasingly resistant to enzyme action. Cellulases produced on different substrates vary in their ratios of Cx to Ci action (Table IV). We hoped, therefore, that use of the resistant residues remaining after enzyme attack, as a substrate for enzyme production, might result in a preparation having a high activity on resistant cellulose. This would have additional advantages in a prac-... 

In the hydrolysis of O-(carboxymethyl) cellulose with acids, the viscosity-molecular weight relationship deviates from the modified Staud-inger equation in a way analogous to that for other cellulosic materials, and the polysaccharide is hydrolyzed enzymically by cellulase similarly to 0-(2-hydroxyethyl) cellulose, so that the two substituents are equally effective in limiting the enzymic action. 

Most fibres made from regenerated cellulose such as viscose, lyocell, and Celsol are characterised by stiffness as well as a fuzzy and uneven surface that makes fabrics susceptible to pilling, even over a short period of use. In order to modify the surface properties of cellulosic fibres and fabrics and to improve their quality biotechnological approaches based on specialised enzymes are widely used. Finishing processes, employing cellulases and xylanases, can replace a number of mechanical and chemical operations, which have been applied until now to improve comfort and quality of fibres and textiles. The principle of enzyme action in the finishing process is controlled hydrolysis of cellulose, in which impurities and fuzz are removed from the surface of fibres, without decreasing their mechanical tenacity or the elasticity of the fabric. 

Structural features met in some cellulases include an a,a barrel111 similar to that of glucoamylase (Fig. 2-29) and, in a cellobiohydrolase,101 a 5-nm-long tunnel into which the cellulose chains must enter. Ten well-defined subsites for glycosyl units are present in the tunnel.101 A feature associated with this tunnel is processive action, movement of the enzyme along the chain without dissociation,105 a phenomenon observed long ago for amylases (see Section 9) and often observed for enzymes acting on nucleic acids. 

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