Information pertaining to enzymatic hydrolysis of cellulose by noncomplexed cellulase enzyme systems is reviewed with a particular emphasis on development of aggregated understanding incorporating substrate features in addition to concentration and multiple cellulase components. Topics considered include properties of cellulose, adsorption, cellulose hydrolysis, and quantitative models. A classification scheme is proposed for quantitative models for enzymatic hydrolysis of cellulose based on the number of solubilizing activities and substrate state variables included. We suggest that it is timely to revisit and reinvigorate functional modeling of cellulose hydrolysis, and that this would be highly beneficial if not necessary in order to bring to bear the large volume of information available on cellulase components on the primary applications that motivate interest in the subject.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/bit.20282

Toward an aggregated understanding of enzymatic hydrolysis of cellulose: noncomplexed cellulase systems.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/jps.2600590523

Determination of tablet strength by the diametral compression test

Publisher Summary The chapter focuses on the recent advances in understanding the structural and functional organization of individual cellulases, their regulation, and the ways in which the multiple enzyme components of cellulolytic systems cooperate. It overviews the cellulose structures because cellulose is more than a homopolymer of β-1 ,4 linked glucose units. An appreciation of its complex physical organization and its interactions with other plant cell wall components is central for understanding of the mechanisms of cellulase action. Cellulose nearly always occurs in close association with plant cell wall matrix polysaccharides so that enzymes such as xylanases are intimately involved in the attack of cellulose in vivo. Cellulases effect important changes to their substrate before releasing soluble products and the key to understanding cellulase action rest in the examination of these events. Progress in this area is limited by the availability of appropriate analytical tools although new techniques, such as atomic force microscopy are promising. The properties of cellulases are profoundly altered by the presence of trace enzyme contaminants. Future studies in vitro are proposed to be restricted to enzymes from recombinant sources. The reasons for the individual cellulolytic bacteria and fungi requiring many related cellulases with specificities that overlap is still not clear, but perhaps this is because the complexity of the substrates and of the task these microorganisms face is underestimated.

Cellulose hydrolysis by bacteria and fungi

Enzymatic hydrolysis of cellulose: An overview

Heterogeneous cellulose accessibility is an important substrate characteristic, but all methods for determining cellulose accessibility to the large-size cellulase molecule have some limitations. Characterization of cellulose accessibility to cellulase (CAC) is vital for better understanding of the enzymatic cellulose hydrolysis mechanism (Zhang and Lynd, Biotechnol. Bioeng. 2004, 88, 797-824; 2006, 94, 888-898). Quantitative determination of cellulose accessibility to cellulase (m2/g of cellulose) was established based on the Langmuir adsorption of the fusion protein containing a cellulose-binding module (CBM) and a green fluorescent protein (GFP). One molecule of the recombinant fusion protein occupied 21.2 cellobiose lattices on the 110 face of bacterial cellulose nanofibers. The CAC values of several cellulosic materials -- regenerated amorphous cellulose (RAC), bacterial microcrystalline cellulose (BMCC), Whatman No. 1 filter paper, fibrous cellulose powder (CF1), and microcrystalline cellulose (Avicel) -- were 41.9, 33.5, 9.76, 4.53, and 2.38 m2/g, respectively. The CAC value of amorphous cellulose made from Avicel was 17.6-fold larger than that of crystalline cellulose - Avicel. Avicel enzymatic hydrolysis proceeded with a transition from substrate excess to substrate limited. The declining hydrolysis rates over conversion are mainly attributed to a combination of substrate consumption and a decrease in substrate reactivity. Declining heterogeneous cellulose reactivity is significantly attributed to a loss of CAC where the easily hydrolyzed cellulose fraction is digested first.

Quantitative determination of cellulose accessibility to cellulase based on adsorption of a nonhydrolytic fusion protein containing CBM and GFP with its applications.

Four grades of coamercially available microcrystalline cellulose have been examined and the appearance, particle size distributions, specific surface areas, pore size distributions and surface energies determined. The median Stokes diamsters ahow general correlation with published data, but Coulter counter results are larger by a factor of approximately 1.4. Correlation is also seen with values obtained from air permeametry experiments.Scanning electron-microscopy demonstrated the presence of two general types of particle, one roughly rod-like and the other an irregular mass. At higher magnifications, fully hydrolysed samples show a microfibrillar structure, the individual fibrils possessing a transparent longitudinal axis. The possibility that the fibrils are hollow is confirmed by analysis of the adsorption isotherms using mathematical models which indicate that the materials are porous, With a modal radius value of about 2.0 nm.

Some Physical Characteristics of Microcrystalline Cellulose 1. Powders for Pharmaceutical Use

“Crushing-Strength” of Compressed Tablets I: Comparison of Testers

Conflicting opinions have been expressed on the flow properties of microcrystalline cellulose powders. Fox, Richman & others (1963) using a commercial grade of microcrystalline cellulose, Avicel (F.M.C. Corporation, Marcus Hook, Pa.), concluded that these powders were free flowing. Later work (Mendell, 1972; Bolhuis & Lerk, 1973) showed that two grades of Avicel, P H 101 and PH 102, possessed very poor flow properties. To clarify this situation, we have examined the flow properties of the tableting grades of Avicel, the two mentioned in the previous paragraph and grades PH 103 and P H 105, by three different techniques. A direct measurement, simulating conditions in feeding the dies of a tablet machine, namely that of the vertical flow of the powder through an orifice, was used. From this the minimum aperture size through which flow would take place was determined. An indirect method of measurement, the Jenike shear cell, was also used. This enabled the coefficient of internal friction, the cohesiveness and the Jenike flow factor to be found. This factor indicates the resistance to flow once this has been initiated and decreases in value as the cohesiveness of the powder increases. Our procedure for the determination of the angle of repose of these powders was based essentially on that of Train (1958) and used the fixed height and fixed base techniques. As the Avicels would not flow freely, Train’s original method had to be slightly modified in that the powder was allowed to flow from a tube 38 mm diameter for the fixed height method. No simple reproducible technique could be found for the

Keith Marshall

Papers

Some Physical Characteristics of Microcrystalline Cellulose 1. Powders for Pharmaceutical Use

“Crushing-Strength” of Compressed Tablets I: Comparison of Testers

The flow properties of microcrystalline cellulose powders.