Isomaltase () is an enzyme that breaks the bonds linking saccharidess, which cannot be broken by amylase or maltase. It digests polysaccharides at the alpha 1-6 linkages. Its substrate, alpha-limit dextrin, is a product of amylopectin digestion that retains its 1-6 linkage (its alpha 1-4 linkages having already been broken down by amylase). The product of the enzymatic digestion of alpha-limit dextrin by isomaltase is maltose.

Isomaltase helps amylase to digest alpha-limit dextrin to produce maltose. The human sucrase-isomaltase is a dual-function enzyme with two GH31 domains, one serving as the isomaltase, the other as a sucrose alpha-glucosidase.

Nomenclature

The systematic name of sucrase-isomaltase is oligosaccharide 6-alpha-glucohydrolase. This enzyme is also known as:

• Sucrase-alpha-dextrinase

• oligo-1,6-glucosidase,

• limit dextrin,

• so maltase,

• exo-oligo-1,6-glucosidase,

• dextrin 6alpha-glucanohydrolase,

• alpha-limit dextrin,

• dextrin 6-glucanohydrolase, and

• oligosaccharide alpha-1,6-glucohydrolase.

Mechanism

This enzyme catalyses the following chemical reaction

1. Hydrolysis of (1->6)-alpha-D-glucosidic linkages in some oligosaccharides produced from starch and glycogen by enzyme EC 3.2.1.1.

Hydrolysis uses water to cleave chemical bonds. Sucrase-isomaltase’s mechanism results in a net retention of configuration at the anomeric center.

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