Cellulolytic enzymes, structure

Besides cellulolytic enzyme lignin, the so-called Bjorkman lignin, alternatively referred to as "milled wood lignin" (MWL) is the best preparation known so far, and it has been widely used for structural studies. When wood meal is ground in a ball mill either dry or in the presence of nonswelling solvents, e.g., toluene, the cell structure of the wood is destroyed and a portion of lignin (usually not more than 50%) can be obtained from the suspension by extraction with a dioxane-water mixture. MWL preparations always contain some carbohydrate material. 

Fiserova M, Suty L (1980) Comparative studies on milled wood lignins and cellulolytic enzyme lignin of beech wood (Fagus silvatica L ) Cellul Chem Technol 14 243-252 Glasser WG, Barnett CA (1979) The structure of lignins in pulps II A comparative evaluation of isolation methods Holzforschung 33 78-86... 

Occurrence, formation, structure and reactions, Wiley-Interscience, New York, 433-485 Chang H-m, Cowling EB, Brown W, Adler E, Miksche G (1975) Comparative studies on cellulolytic enzyme lignin and milled wood lignin of sweetgum and spruce. Holzforschung 29 153-159... 

This initial oxidative depolymerization of cellulose evidently opens up the wood cell wall structure so that cellulolytic and hemi-cellulolytic enzymes can reach their substrates despite the presence of lignin. Solubility of wood in 1% NaOH increases markedly on brown-rot attack IS) and reflects cellulose depolymerization and the opening up of the wood structure. 

Improved protein separation techniques utilizing hquid chromatography and electrophoresis coupled with X-ray diffraction and NMR studies have given insights into the three-dimensional structures of cellulolytic enzymes. This molecular architecture data coupled with DNA sequence information has given clues to the chemical mechanisms of enzymatic hydrolysis and molecular interaction between cellulose and the enzymes. 

Work needs to be done to find the specific activity of purified enzymes on the cellulose structure, especially the synergism between different cellulolytic enzymes. With this understood, one can then undertake the task of studying the endoglucanase-cellobiohydrolase system. This requires the identification of binding sites, reaction sites, and changes in cellulose structure as a result of the enzyme action. 

Size and Diffusibility of Cellulolytic Enzymes in Relation to the Capillary Structure of Cellulose. As discussed earlier, enzymatic degradation of cellulose requires that the cellulolytic and other extracellular enzymes of the organisms diffuse from the organism producing them to accessible surfaces on or in the walls of the fiber. This accessible surface is defined by the size, shape, and surface properties of the microscopic and submicroscopic capillaries within the fiber in relation to the size, shape, and diffusibility of the enzyme molecules themselves. The influence of these relationships on the susceptibility and resistance of cellulose to enzymatic hydrolysis has not been verified experimentally in natural fibers but the validity of the concepts that follow is demonstrated by the work of Stone, Scallan, Donefer, and Ahlgren (69). 

In addition to considerations of size and shape, the surface properties of the fiber capillaries and the diffusibility of the cellulolytic enzyme molecules within them can profoundly influence the susceptibility of cellulose to enzymatic hydrolysis. In contrast to inorganic catalysts, enzymes have a very strong and specific affinity for their specific substrate molecules. This affinity accounts for their susceptibility to competitive inhibitors. When the substrate exists as an insoluble polymer in a complex structural matrix, this specific affinity drastically reduces the rate of diffusion of the enzyme in the presence of the substrate. This retarded... 

One possible explanation for these different modes of cellulose depolymerization in the same species of wood is that the cellulolytic enzyme molecules of Poria monticola are smaller than those of Polyporus versicolor and for that reason would be able to penetrate and act in regions of the fine structure of the fibers that are not accessible to those of the latter fungus. This hypothesis has led to efforts (as yet incomplete) to determine the molecular size of the cellulolytic enzyme proteins of these two organisms. Another possible explanation is that the initial dissolution of cellulose and other cell-wall polysaccharides is accomplished by catalysts that are not enzyme proteins and therefore could be substantially smaller in molecular size. Halliwell (21) has described experiments on the... 

Due to the amorphous structure, ANP acquires such specific features as increased content of functional groups, high accessibility, and sorption ability (loelovich, 2013a, 2014a). Freeze-dried amorphous nanocellulose has an enhanced wetting enthalpy (—125 to — 130J/g), absorbs up to 35—40% water vapor, and completely decomposes under action of cellulolytic enzymes. Moreover, the chemical modification of ANP is carried out faster and deeper than other kinds of nanocellulose. 

Despite the high crystallinity, this kind of nanocellulose exhibits an enhanced enzymatic hydrolyzability, which can be attributed to the high porosity and well-developed surface of the nanostructured bacterial cellulose. Due to these structural features, the BNC sample acquires a high accessibility for molecules of cellulolytic enzymes, which contributes to deep enzymatic hydrolysis of this NC both in never-dried and dry states (loelovich, 2014c). 

Due to the amorphous structure, ANP acquires an enhanced water sorption and wetting enthalpy, as well as complete decomposition under action of cellulolytic enzymes. Increased content of negative-charged sulfonic groups imparts a stable phase state of dilute aqueous dispersions of ANP. Study of rheological... 

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