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Cellulase
 
 
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Cellulase refers to a class of enzymes produced chiefly by fungi, bacteria
Bacteria

The Bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals....
, and protozoans that catalyze the cellulolysis (or hydrolysis
Hydrolysis

Hydrolysis is a chemical reaction during which one or more water are split into hydrogen and hydroxide ions which may go on to participate in further reactions....
) of cellulose
Cellulose

File:Cellulose Sessel.svgCellulose is an organic compound with the chemical formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand ? linked D-glucose units....
. However, there are also cellulases produced by other types of organisms such as plants and animals. Several different kinds of cellulases are known, which differ structurally and mechanistically. The EC number
EC number

The Enzyme Commission number is a numbering scheme scheme for enzymes, based on the chemical reactions they catalysis.As a system of enzyme nomenclature, every EC number is associated with a recommended name for the respective enzyme....
 for this group of enzymes is .

Reaction: Hydrolysis of 1,4-beta-D-glycosidic linkages in cellulose, lichenin and cereal beta-D-glucans.

Other names: Various names for the type 'endoglucanases' are: endo-1,4-beta-glucanase, carboxymethyl cellulase (CMCase), endo-1,4-beta-D-glucanase, Beta-1,4-glucanase, Beta-1,4-endoglucan hydrolase, Celludextrinase.






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Cellulase refers to a class of enzymes produced chiefly by fungi, bacteria
Bacteria

The Bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals....
, and protozoans that catalyze the cellulolysis (or hydrolysis
Hydrolysis

Hydrolysis is a chemical reaction during which one or more water are split into hydrogen and hydroxide ions which may go on to participate in further reactions....
) of cellulose
Cellulose

File:Cellulose Sessel.svgCellulose is an organic compound with the chemical formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand ? linked D-glucose units....
. However, there are also cellulases produced by other types of organisms such as plants and animals. Several different kinds of cellulases are known, which differ structurally and mechanistically. The EC number
EC number

The Enzyme Commission number is a numbering scheme scheme for enzymes, based on the chemical reactions they catalysis.As a system of enzyme nomenclature, every EC number is associated with a recommended name for the respective enzyme....
 for this group of enzymes is .

Reaction: Hydrolysis of 1,4-beta-D-glycosidic linkages in cellulose, lichenin and cereal beta-D-glucans.

Other names: Various names for the type 'endoglucanases' are: endo-1,4-beta-glucanase, carboxymethyl cellulase (CMCase), endo-1,4-beta-D-glucanase, Beta-1,4-glucanase, Beta-1,4-endoglucan hydrolase, Celludextrinase. The other types of cellulase belong to Excocellulases. Bet glucosidases can also be considered as yet another group of cellulases. The expression 'Avicelase' refers to the total cellulase activity of a given sample of the enzyme(s). The activity may be the result of the action of more than one type of enzymes.

Types and action

Five general types of cellulases based on the type of reaction catalyzed:
  • Endo-cellulase breaks internal bonds to disrupt the crystalline structure of cellulose and expose individual cellulose polysaccharide chains
  • Exo-cellulase cleaves 2-4 units from the ends of the exposed chains produced by endocellulase, resulting in the tetrasaccharide
    Tetrasaccharide

    A tetrasaccharide is a carbohydrate which gives upon hydrolysis four molecules of the same or different monosaccharides. For example, stachyose upon hydrolysis gives one molecule each of glucose and fructose and two molecules of galactose....
    s or disaccharide
    Disaccharide

    A disaccharide is a sugar composed of two monosaccharides.'Disaccharide' is one of the four chemical groupings of carbohydrates ....
     such as cellobiose
    Cellobiose

    Cellobiose is a disaccharide with the formula [HOCH2CHO3]2O. The molecule is derived from the condensation of two glucose molecules linked in a ? bond....
    . There are two main types of exo-cellulases (or cellobiohydrolases, abbreviate CBH) - one type working processively from the reducing end, and one type working processively from the non-reducing end of cellulose.
  • Cellobiase or beta-glucosidase
    Beta-glucosidase

    Beta-glucosidase is a glucosidase enzyme which acts upon ?1->4 bonds linking two glucose or glucose-substituted molecules . An exocellulase with specificity for a variety of beta-D-glycoside substrates....
     hydrolyses the exo-cellulase product into individual monosaccharides.
  • Oxidative cellulases that depolymerize cellulose by radical reactions, as for instance cellobiose dehydrogenase (acceptor)
    Cellobiose dehydrogenase (acceptor)

    In enzymology, a cellobiose dehydrogenase is an enzyme that catalysis the chemical reactionThus, the two substrate of this enzyme are cellobiose and acceptor, whereas its two product are cellobiono-1,5-lactone and reduced acceptor....
    .
  • Cellulose phosphorylases that depolymerize cellulose using phosphates instead of water.
In the most familiar case of cellulase activity, the enzyme complex breaks down cellulose
Cellulose

File:Cellulose Sessel.svgCellulose is an organic compound with the chemical formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand ? linked D-glucose units....
 to beta-glucose
Glucose

Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
. This type of cellulase is produced mainly by symbiotic bacteria
Bacteria

The Bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals....
 in the ruminating
Ruminant

Physiologically, a ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first stomach, known as the rumen, then regurgitating the semi-digested mass, now known as cud, and chewing it again....
 chambers of herbivore
Herbivore

Herbivory is a form of predation in which an organism, known as an herbivore, heterotrophs principally autotrophs such as plants, algae and photosynthesizing bacteria....
s. Aside from ruminants, most animals (including humans) do not produce cellulase in their bodies, and are therefore unable to use most of the energy contained in plant material. Enzymes which hydrolyze Hemicellulose
Hemicellulose

A hemicellulose can be any of several heteropolymers present in almost all plant cell walls along with cellulose. While cellulose is crystalline, strong, and resistant to hydrolysis, hemicellulose has a random, amorphous structure with little strength....
 are usually referred to as hemicellulase and are usually classified under cellulase in general. Enzymes that cleave lignin
Lignin

Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae....
 are occasionally classified as cellulase, but this is usually considered erroneous.

Within the above types there are also progressive (also known as processive) and non-progressive types. Progressive cellulase will continue to interact with a single polysaccharide strand, non-progressive cellulase will interact once then disengage and engage another polysaccharide strand.

Most fungal cellulases have a two-domain structure with one catalytic domain, and one cellulose binding domain, that are connected by a flexible linker. This structure is adaption for working on an insoluble substrate and it allows the enzyme to diffuse two-dimensionally on a surface in a caterpillar way. However, there are also cellulases (mostly endoglucanases) that lacks cellulose binding domain. These enzymes might have a swelling function.

Mechanism of cellulolysis

Types of Cellulase2
Cellulase Mech

Uses

Cellulase is used for commercial food processing in coffee
Coffee

Coffee is a brewed drink prepared from roasted seeds, commonly called coffee beans, of the Coffea. Caffeinated coffee has a stimulating effect in humans....
. It performs hydrolysis
Hydrolysis

Hydrolysis is a chemical reaction during which one or more water are split into hydrogen and hydroxide ions which may go on to participate in further reactions....
 of cellulose during drying of beans
Coffee bean

A coffee bean is the seed of the Coffea . The fruits, coffee cherries or coffee berries, most commonly contain two stones with their flat sides together....
. Furthermore, cellulases are widely used in textile industry and in laundry detergents. They have also been used in the pulp and paper industry for various purposes, and they are even used for pharmaceutical applications. Cellulase is used in the fermentation of biomass
Biomass

Biomass, as a renewable energy source, refers to living and recently dead biological material that can be used as fuel or for industrial production....
 into biofuels, although this process is relatively experimental at present. Cellulase is used as a treatment for Phytobezoars, a form of cellulose bezoar
Bezoar

A bezoar is a mass found trapped in the gastrointestinal system , though they can occur in other locations.There are several varieties of bezoar, some of which have inorganic constituents and others organic compound....
 found in the human stomach
Stomach

In most mammals, the stomach is a hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication....
.

See also

  • Hemicellulose
    Hemicellulose

    A hemicellulose can be any of several heteropolymers present in almost all plant cell walls along with cellulose. While cellulose is crystalline, strong, and resistant to hydrolysis, hemicellulose has a random, amorphous structure with little strength....