Glucanases are enzymes that break down large polysaccharides via hydrolysis. The product of the hydrolysis reaction is called a glucan, a linear polysaccharide made of up to 1200 glucose monomers, held together with glycosidic bonds. Glucans are abundant in the endosperm cell walls of cereals such as barley, rye, sorghum, rice, and wheat. Glucanases are also referred to as lichenases, hydrolases, glycosidases, glycosyl hydrolases, and/or laminarinases. Many types of glucanases share similar amino acid sequences but vastly different substrates. Of the known endo-glucanases, 1,3-1,4-β-glucanase is considered the most active. Structure β-glucanases The secondary and tertiary structures of β-glucanases involves the stacking of multiple β-sheets, each of which are made of several anti-parallel strands that bend and form a cleft crossing the active site of the enzyme. This type of structure has been called the "jelly roll fold." Some common β-glucanases 1,3-β-glucanases (laminarinases, EC 3.2.1.39) Endo-1,3(4)-β-glucanase β-1,3-glucanase, an enzyme in plants that breaks down β-1,3-glucans such as callose or curdlan β-1,6 glucanase, an enzyme that breaks down β-1,6-glucans Cellulase, an enzyme that perform the hydrolysis of 1,4-beta-D-glycosidic linkages in cellulose, lichenin and cereal β-D-glucans. Xyloglucan-specific endo-beta-1,4-glucanase Xyloglucan-specific exo-beta-1,4-glucanase α-glucanases α-1,4-glucanase, an enzyme that breaks down α-1,4-glucans α-1,6-glucanase, an enzyme that breaks down α-1,6-glucans Pullulanase, a specific kind of glucanase that degrade pullulan The functional formation of the enzyme-substrate complex is dictated by the induced-fit mechanism. Mechanism of Enzyme Action The main function of glucanase is to catalyze the hydrolysis of glycosidic bonds in polysaccharides. This function is not highly specific, and the enzymes distinguish among substrates mostly by the types of bonds present and α- or β- configuration. In 1953, Dr. D. E. Koshland proposed a double-displacement mechanism for this enzyme action. The first step of his proposed mechanism is rate-limiting step independent of the concentration of the substrate and involves an amino acid nucleophile and an acid/base catalyst. In this step, the nucleophile, with help from the acid residue, displaces the aglycone and forms a covalent glycosyl-enzyme intermediate. The second step involves a water molecule, assisted by the conjugate base of the acid catalyst, rendering the free sugar while retaining an anomeric configuration of the molecule. Glucanases can also catalyze transglycosylation, resulting in new β-glycosidic bonds between donor and acceptor saccharides. This reaction, which has the same region- and stereo-specificity as the hydrolysis reaction, involves either the direct reversal of hydrolysis (known as condensation) or kinetic control of a glycosyl