Cellulose, enzymatic degradation

The plant cell wall is a polymeric mesh consisting of cellulose, hemicellulose, pectin and protein. Cellulose and hemicellulose are integral components of the cell wall, but pectic substances are located mainly in the outer wall regions within the middle lamella (McNeil et ai, 1984). Pectic substances are more susceptible to enzymatic degradation, because they are more exposed than other cell wall components. Therefore, pectin-degrading enzymes may play a central role in the penetration of plant tissue by bacteria. 

Hamacher, K. and Sahm, H., Characterization of enzymatic degradation products of carboxymethyl cellulose by gel permeation chromatograph, Carb. Polym., 5, 319, 1985. 

Cellulose is found in nature in combination with various other substances, the nature and composition of which depend on the source and previous history of the sample. In most plants, there are three major components cellulose, hemicelluloses, and lignin. Efficient utilization of all three components would greatly help the economics of any scheme to obtain fuel from biomass. Hemicelluloses, lignocellulose and lignin remaining after enzymatic degradation of the cellulose in wood would require chemical or thermal treatment - as distinct from biochemical - to produce a liquid fuel. 

A few animals (especially ruminants and termites) are able to metabolize cellulose, but even these animals depend on appropriate microorganisms in their intestinal tracts to hydrolyze the -1,4 links other animals, including man, cannot utilize cellulose as food because they lack the necessary hydrolytic enzymes. However, such enzymes are distributed widely in nature. In fact, deterioration of cellulose materials —textiles, paper, and wood —by enzymatic degradation (such as by dry rot) is an economic problem that is not yet adequately solved. Efforts to turn this to advantage through enzymatic hydrolysis of cellulose to glucose for practical food production have not been very successful (see Section 25-12). 

Influence of Cellulose Physical Structure on Thermohydrolytic, Hydrolytic, and Enzymatic Degradation of Cellulose... 

In this context, some experimental results relevant to these open questions of enzymatic degradation will be presented and will be discussed from the viewpoint of cellulose chemistry, together with a summary of our recent work on thermohydrolysis and acid hydrolysis of cellulose, performed in connection with research on cellulose powder manufacture (7). After a short survey of the experimental techniques applied, this contribution will be centered on three problems (1) the interaction of chain degradation and cross-linking in thermal and thermo-hydrolytic treatments of cellulose, (2) the influence of mechanical strain... 

Table VIII. Enzymatic Degradation of Cellulose Powders of Different Origin and Particle Size (Cellulose T, 1% Substrate 68 hr 40°C)...

Table X. Influence of NH3 Pretreatment and of Mercerization on Enzymatic Degradation of Cellulose Powders...

Further progress in understanding this effect, as well as others, of the physical structure of cellulose on enzymatic degradation may be expected from combining physicochemical and morphological techniques and from kinetic measurements in heterogeneous enzymatic hydrolysis, applying substrates of well-defined physical structure and isolated components of the enzyme systems. 

The Mode of Enzymatic Degradation of Cellulose Based on the Properties of Cellulase Components... 

The cellulosic material S0 is composed of amorphous matter Sa, crystalline matter Sc, and nonhydrolyzable merts Sx, and their rates of enzymatic degradation are different. 

As an example using NMMO solution, the spinning of fibers consisting of blends of cellulose with cationic starch was investigated for the purpose of improving moisture absorbability, dyeability, and enzymatic degradability compared with standard Lyocell fibers [69]. 

Nidetzky, B., Steiner, W., and Claeyssens, M. 1995. Synergistic interaction of cellulases from Trichoderma reesei during cellulose degradation. Enzymatic Degradation of Insoluble Carbohydrates. ACS Symposium Series, 618, 90-112. 

At present cellobiose is not a practical substrate for amylose production, but the enzymatic degradation of cellulose is extensively studiedand the conversion of cellobiose into amylose by the CBP-GP system should be the important way to convert cellulosic biomass into value-added materials and products. 

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