Cellulose breakdown is of considerable economic importance, because it makes a major constituent of plants available for consumption and use in chemical reactions.

Because cellulose molecules bind strongly to each other, cellulolysis is relatively difficult compared to the breakdown of other polysaccharides such as starch.

In many herbivorous animals such as ruminants like cattle and sheep and hindgut fermenters like horses, cellulases are produced by symbiotic bacteria.

Aside from ruminants, most animals (including humans) do not produce cellulase in their bodies and can only partially break down cellulose through fermentation, limiting their ability to use energy in fibrous plant material.

This structure is adapted for working on an insoluble substrate, and it allows the enzyme to diffuse two-dimensionally on a surface in a caterpillar-like fashion.

Both binding of substrates and catalysis depend on the three-dimensional structure of the enzyme which arises as a consequence of the level of protein folding.

[9] The Thermotoga maritima species make cellulases consisting of 2 β-sheets (protein structures) surrounding a central catalytic region which is the active-site.

[10] The enzyme is categorised as an endoglucanase, which internally cleaves β-1,4-glycosydic bonds in cellulose chains facilitating further degradation of the polymer.

[10] Cellulases produced by the species Coprinopsis cinerea consists of seven protein strands in the shape of an enclosed tunnel called a β/α barrel.

For example, Clostridium cellulolyticum produces 13 GH9 modular cellulases containing a different number and arrangement of catalytic-domain (CD), carbohydrate-binding module (CBM), dockerin, linker and Ig-like domain.

Cellulases affect the fiber morphology, which may lead to improved fibre-fibre bonding, resulting in increased fibre cohesion.

[18] Additional effects on the paper may include increased tensile strength, higher bulk, porosity and tissue softness.

Cellulase is used in medicine as a treatment for phytobezoars, a form of cellulose bezoar found in the human stomach, and it has exhibited efficacy in degrading polymicrobial bacterial biofilms by hydrolyzing the β(1-4) glycosidic linkages within the structural, matrix exopolysaccharides of the extracellular polymeric substance (EPS).

The ancillary enzyme present in the reagent mixture (β-glucosidase) then acts to hydrolyse the fragment containing the chromophore or fluorophore.