Isoamylase

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Introductions

Isoamylase is an enzyme with systematic name glycogen 6-alpha-D-glucanohydrolase. This enzyme catalyses the following chemical reaction. Hydrolysis of (1->6)-alpha-D-glucosidic branch linkages in glycogen, amylopectin and their beta-limit dextrins.

Functions

Isoamylase hydrolyzes only the -1,6 glycosidic chain at the branching point of glycogen or branched starch, cutting off the entire side branch and forming straight-chain starch of varying length. The characteristics of the action of isoamylase on the substrate can be confirmed by the properties of the product after its action on glutinous rice starch. When isoamylase acts on glutinous rice starch, with the unbranching action, the iodine color reaction changes from red to blue, the reducing power increases, precipitation occurs in butanol, the starch solution becomes easily aged, and the characteristics of straight-chain starch appear. A striking phenomenon when isoamylase is used in combination with other amylases is that it leads to complete saccharification of starch.

Discovery

Isoamylase was discovered in yeast extracts as early as 1940, but the enzymatic properties of isoamylase have been known for a not too short period of time. The enzyme interacts with glutinous rice starch solution. It can cause turbidity. After a few days, a white precipitate occurs, which gradually changes to blue if reacted with iodine. This change in iodine reaction is the opposite of the change in the decomposition of starch by acid and amylase, etc. Therefore, the enzyme was mistakenly thought to have the function of synthesizing starch, and was named starch synthase. Later. With the advancement of starch chemistry, the amylase was better understood. We realized that the color change of the above iodine reaction was related to the properties of branched chain starch and straight chain starch, and the so-called starch synthase was actually an enzyme that cut the '6 glycosidic bond. We renamed this enzyme as isoamylase.

Distribution

Isoamylase is widely found in nature. In plants. Isoamylase is found in rice, broad beans, potatoes, malt and sweet corn. In the liver and muscle of higher animals, there are also enzymes that break down the II-1,6 glycosidic bond similar to isoamylase. There are many strains of microorganisms that can produce isoamylase. In addition to yeast, many bacteria and some actinomycetes have been found to produce isoamylase. Moreover, it is known that different sources of isoamylases differ in their specificity of action on the substrate.

Applications

The main application of isoamylase is in the decomposition of various branched polysaccharides and thrombomycin. By the 1970s, the application of isoamylase has been extended to various starch deep processing fields such as starch syrup, beer and alcohol production, and gradually moved from the laboratory stage to the industrial scale. In starch processing, isoamylase can accelerate the saccharification process and improve the saccharification rate when it works in synergy with glycosylase; when it works in combination with β-amylase, it can greatly improve the maltose yield, so it is a branched chain amylase in great demand. At present, it has been successfully applied in the production of high glucose syrup, high maltose syrup and beer.