Amylose is a spiral structure without branches, which consists of glucose residues connected end to end only by α- 1, 4- glucoside bond. Each chain of amylopectin is composed of glucose residues connected end to end by α- 1, 4- glycosidic bond, but it is α- 1, 6- glycosidic bond at the branch.
1.α- amylase and its function
Alpha-amylase, also known as endoamylase, is a kind of metal hydrolase that needs calcium ions. Calcium ion binds to enzyme protein and shows activity, but EDTA treatment will make its activity lose.
α -amylase can randomly hydrolyze α- 1, 4- glycosidic bonds in starch, but it cannot hydrolyze α- 1, 6- glycosidic bonds. If the substrate is amylose, it will hydrolyze to produce glucose, maltose and maltotriose; If the substrate is amylopectin, the hydrolysate is glucose, maltose, maltotriose and α-dextrin with α- 1, 6- glycosidic bond, with more than 3 glucose residues.
In addition, it should be noted that α and β in α -amylase and β -amylase do not represent any conformational relationship, but are just numbered. There are many ways to produce α -amylase in nature, for example, microbial fermentation is the most commonly used method. In addition, this enzyme can also be extracted from plants or animals, and the properties of amylase obtained by different ways are different. Because of the great demand for α -amylase in industrial production, fungi and bacteria are generally used for fermentation. Bacillus subtilis, Bacillus and Streptomyces hygroscopicus can all produce α -amylase
2. β -amylase and its function
β-amylase, also known as exoamylase, is a kind of hydrolase containing sulfhydryl groups. Starting from the non-reducing end of starch, the enzyme hydrolyzes α- 1, 4- glycosidic bond in turn in units of two glucose residues to produce maltose, but it can't hydrolyze α- 1, 6- glycosidic bond, so it can't go beyond the fulcrum and leave a very long dextrin, that is, β-dextrin. Therefore, when β -amylase acts on amylose, almost only maltose is produced; When used in amylopectin, the products are maltose and β -dextrin
3.R- enzyme and its function
R- enzyme, also called debranching enzyme, acts on α- 1, 6- glycosidic bond. Under the action of debranching enzyme, the α- 1, 6- glycosidic bond of α-dextrin and β-dextrin is hydrolyzed and the branched chain is removed. The remaining linear part is hydrolyzed by α -amylase and β -amylase to produce maltose and glucose. However, R- enzyme can not directly hydrolyze α- 1, 6- glycosidic bond in amylopectin.
4. Glycosylated amylase and its function
Saccharifying amylase, glucoamylase, is an enzyme that can hydrolyze starch into glucose, in which the hydrolysis rate can reach 100%, and it is usually used as a saccharifying agent for starch. Glucoamylase has low specificity and is suitable for many substances. It can cleave both α- 1, 4- glycosidic bonds and α- 1, 6- glycosidic bonds from the non-reducing end of starch molecules, but the hydrolysis speed of α- 1, 4- glycosidic bonds is faster. At the same time, it can hydrolyze dextrin, maltose and glycogen. Hydrolysis starts from the end of the substrate molecule and belongs to exonuclease.