sucrase-isomaltase; invertase; beta-fructofuranosidase; limit dextrinase; palatinase (SI)

Function

• role in the final stage of carbohydrate digestion
• hydrolysis of (1->6)-alpha-D-glucosidic linkages in some oligosaccharides produced from starch & glycogen by alpha-amylase, & in isomaltose

Structure

• sulfated (putative)
• belongs to the glycosyl hydrolase 31 family contains 1 P-type (trefoil) domain
• sucrase & isomaltase subunits stay associated with one another in a complex by non-covalent linkages
• precursor is proteolytically cleaved when exposed to pancreatic proteases in the intestinal lumen
• hydrolysis of sucrose & maltose by an alpha- D-glucosidase-type action

Compartment

• apical cell membrane
• brush border

Expression

• expressed in the poorly differentiated crypt cells of the small intestine as well as in the mature villous cells
• expressed at very low levels in the colon

Pathology

• defects in SI are the cause of congenital sucrase-isomaltase deficiency

Genetics

• there is a high degree of homology between the isomaltase & sucrase portions (41% of amino acid identity) indicating that this protein is evolved by partial gene duplication

More general terms

• glycosidase (glycoside hydrolase)
• glycoprotein
• membrane protein

More specific terms

• sacrosidase (Sucraid)

Database

• UniProt: http://www.uniprot.org/uniprot/P14410.html
• Entrez gene: http://www.ncbi.nlm.nih.gov/sites/entrez?db=gene&cmd=Retrieve&dopt=Graphics&list_uids=6476
• Kegg: http://www.genome.jp/dbget-bin/www_bget?hsa:6476
• OMIM: https://mirror.omim.org/entry/222900
• OMIM: https://mirror.omim.org/entry/609845