Isomaltase

Isomaltase (EC 3.2.1.10) is an enzyme that breaks the bonds linking saccharides, 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.

Oligo-1,6-glucosidase
Identifiers
EC number3.2.1.10
Databases
IntEnzIntEnz view
BRENDABRENDA entry
ExPASyNiceZyme view
KEGGKEGG entry
MetaCycmetabolic pathway
PRIAMprofile
PDB structuresRCSB PDB PDBe PDBsum

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 dextrine,
  • so maltase,
  • exo-oligo-1,6-glucosidase,
  • dextrin 6alpha-glucanohydrolase,
  • alpha-limit dextrine,
  • dextrin 6-glucanohydrolase, and
  • oligosaccharide alpha-1,6-glucohydrolase.

Mechanism
Mechanism for how sucrase-isomaltase catalyzes the conversion of isomaltose to two glucose molecules

This enzyme catalyses the following chemical reaction

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.[1]


References
  1. Sim L, Willemsma C, Mohan S, Naim HY, Pinto BM, Rose DR (June 2010). "Structural basis for substrate selectivity in human maltase-glucoamylase and sucrase-isomaltase N-terminal domains". The Journal of Biological Chemistry. 285 (23): 17763–70. doi:10.1074/jbc.M109.078980. PMC 2878540. PMID 20356844.


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