- 唾液腺αアミラーゼ
- 膵αアミラーゼ
- マルターゼ・グルコアミラーゼ（小腸）
- スクラーゼ・イソマルターゼ（小腸）
- リソソームαグルコシダーゼ
Maltase-glucoamylase, intestinal
Functioni
May serve as an alternate pathway for starch digestion when luminal alpha-amylase activity is reduced because of immaturity or malnutrition. May play a unique role in the digestion of malted dietary oligosaccharides used in food manufacturing.
Catalytic activityi
Hydrolysis of terminal, non-reducing (1->4)-linked alpha-D-glucose residues with release of alpha-D-glucose.
Hydrolysis of terminal (1->4)-linked alpha-D-glucose residues successively from non-reducing ends of the chains with release of beta-D-glucose.
Including the following 2 domains:
Maltase
EC=3.2.1.20
Alternative name(s):
Alpha-glucosidase
Glucoamylase
EC=3.2.1.3
Alternative name(s):
Glucan 1,4-alpha-glucosidase
Gene names
Name: MGAM
Synonyms: MGA, MGAML
Function
May serve as an alternate pathway for starch digestion when luminal alpha-amylase activity is reduced because of immaturity or malnutrition. May play a unique role in the digestion of malted dietary oligosaccharides used in food manufacturing.
Catalytic activity
Hydrolysis of terminal, non-reducing (1->4)-linked alpha-D-glucose residues with release of alpha-D-glucose.
Hydrolysis of terminal (1->4)-linked alpha-D-glucose residues successively from non-reducing ends of the chains with release of beta-D-glucose.
Subunit structure
Monomer.
Subcellular location
Apical cell membrane; Single-pass type II membrane protein. Note: Brush border.
Tissue specificity
Expressed in small intestine, granulocyte, and kidney but not in salivary gland or pancreas.
Post-translational modification
N- and O-glycosylated. Ref.7
Does not undergo intracellular or extracellular proteolytic cleavage.
Sulfated By similarity.
Sequence similarities
Belongs to the glycosyl hydrolase 31 family.
Contains 2 P-type (trefoil) domains.
Alpha-amylase 1
EC=3.2.1.1
Alternative name(s):
1,4-alpha-D-glucan glucanohydrolase 1
Salivary alpha-amylase
Catalytic activity
Endohydrolysis of (1->4)-alpha-D-glucosidic linkages in polysaccharides containing three or more (1->4)-alpha-linked D-glucose units.
Cofactor
Binds 1 calcium ion per subunit.
Binds 1 chloride ion per subunit.
Subunit structure
Monomer.
Subcellular location
Secreted.
Sequence similarities
Belongs to the glycosyl hydrolase 13 family.
Pancreatic alpha-amylase
Short name=PA
EC=3.2.1.1
Alternative name(s):
1,4-alpha-D-glucan glucanohydrolase
Gene names
Name: AMY2A
Catalytic activity
Endohydrolysis of (1->4)-alpha-D-glucosidic linkages in polysaccharides containing three or more (1->4)-alpha-linked D-glucose units.
Cofactor
Binds 1 calcium ion per subunit.
Binds 1 chloride ion per subunit.
Subunit structure
Monomer.
Subcellular location
Secreted › extracellular space.
Sequence similarities
Belongs to the glycosyl hydrolase 13 family.
Sucrase-isomaltase, intestinal
Cleaved into the following 2 chains:
Sucrase
EC=3.2.1.48
Isomaltase
EC=3.2.1.10
Function
Plays an important role in the final stage of carbohydrate digestion. Isomaltase activity is specific for both alpha-1,4- and alpha-1,6-oligosaccharides. Ref.7
Catalytic activity
Hydrolysis of sucrose and maltose by an alpha-D-glucosidase-type action.
Hydrolysis of (1->6)-alpha-D-glucosidic linkages in some oligosaccharides produced from starch and glycogen by alpha-amylase, and in isomaltose.
Subunit structure
The resulting sucrase and isomaltase subunits stay associated with one another in a complex by non-covalent linkages.
Subcellular location
Apical cell membrane; Single-pass type II membrane protein. Note: Brush border.
Tissue specificity
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. Ref.5
Post-translational modification
The precursor is proteolytically cleaved when exposed to pancreatic proteases in the intestinal lumen.
Sulfated By similarity.
Involvement in disease
Congenital sucrase-isomaltase deficiency (CSID) [MIM:222900]: Autosomal recessive intestinal disorder that is clinically characterized by fermentative diarrhea, abdominal pain, and cramps upon ingestion of sugar. The symptoms are the consequence of absent or drastically reduced enzymatic activities of sucrase and isomaltase. The prevalence of CSID is 0.02 % in individuals of European descent and appears to be much higher in Greenland, Alaskan, and Canadian native people. CSID arises due to post-translational perturbations in the intracellular transport, polarized sorting, aberrant processing, and defective function of SI.
Note: The disease is caused by mutations affecting the gene represented in this entry. Ref.8 Ref.9 Ref.10 Ref.11 Ref.12
Miscellaneous
There is a high degree of homology between the isomaltase and sucrase portions (41% of amino acid identity) indicating that this protein is evolved by partial gene duplication.
Sequence similarities
Belongs to the glycosyl hydrolase 31 family.
Contains 2 P-type (trefoil) domains.
Beta-galactosidase
EC=3.2.1.23
Alternative name(s):
Acid beta-galactosidase
Short name=Lactase
Elastin receptor 1
Function
Cleaves beta-linked terminal galactosyl residues from gangliosides, glycoproteins, and glycosaminoglycans. Ref.9
Isoform 2 has no beta-galactosidase catalytic activity, but plays functional roles in the formation of extracellular elastic fibers (elastogenesis) and in the development of connective tissue. Seems to be identical to the elastin-binding protein (EBP), a major component of the non-integrin cell surface receptor expressed on fibroblasts, smooth muscle cells, chondroblasts, leukocytes, and certain cancer cell types. In elastin producing cells, associates with tropoelastin intracellularly and functions as a recycling molecular chaperone which facilitates the secretions of tropoelastin and its assembly into elastic fibers. Ref.9
Catalytic activity
Hydrolysis of terminal non-reducing beta-D-galactose residues in beta-D-galactosides.
Subcellular location
Isoform 1: Lysosome.
Isoform 2: Cytoplasm › perinuclear region. Note: Localized to the perinuclear area of the cytoplasm but not to lysosomes.
Involvement in disease
GM1-gangliosidosis 1 (GM1G1) [MIM:230500]: An autosomal recessive lysosomal storage disease marked by the accumulation of GM1 gangliosides, glycoproteins and keratan sulfate primarily in neurons of the central nervous system. GM1-gangliosidosis type 1 is characterized by onset within the first three months of life, central nervous system degeneration, coarse facial features, hepatosplenomegaly, skeletal dysmorphology reminiscent of Hurler syndrome, and rapidly progressive psychomotor deterioration. Urinary oligosaccharide levels are high. It leads to death usually between the first and second year of life.
Note: The disease is caused by mutations affecting the gene represented in this entry. Ref.16 Ref.17 Ref.18 Ref.19 Ref.20 Ref.22 Ref.25 Ref.28 Ref.29 Ref.30 Ref.33 Ref.35 Ref.36 Ref.38 Ref.39 Ref.40 Ref.42
GM1-gangliosidosis 2 (GM1G2) [MIM:230600]: A gangliosidosis characterized by onset between ages 1 and 5. The main symptom is locomotor ataxia, ultimately leading to a state of decerebration with epileptic seizures. Patients do not display the skeletal changes associated with the infantile form, but they nonetheless excrete elevated amounts of beta-linked galactose-terminal oligosaccharides. Inheritance is autosomal recessive.
Note: The disease is caused by mutations affecting the gene represented in this entry. Ref.17 Ref.18 Ref.20 Ref.30 Ref.32 Ref.35 Ref.38 Ref.40 Ref.42
GM1-gangliosidosis 3 (GM1G3) [MIM:230650]: A gangliosidosis with a variable phenotype. Patients show mild skeletal abnormalities, dysarthria, gait disturbance, dystonia and visual impairment. Visceromegaly is absent. Intellectual deficit can initially be mild or absent but progresses over time. Inheritance is autosomal recessive.
Note: The disease is caused by mutations affecting the gene represented in this entry. Ref.17 Ref.18 Ref.21 Ref.22 Ref.24 Ref.31 Ref.37 Ref.38 Ref.40 Ref.42
Mucopolysaccharidosis 4B (MPS4B) [MIM:253010]: A form of mucopolysaccharidosis type 4, an autosomal recessive lysosomal storage disease characterized by intracellular accumulation of keratan sulfate and chondroitin-6-sulfate. Key clinical features include short stature, skeletal dysplasia, dental anomalies, and corneal clouding. Intelligence is normal and there is no direct central nervous system involvement, although the skeletal changes may result in neurologic complications. There is variable severity, but patients with the severe phenotype usually do not survive past the second or third decade of life.
Note: The disease is caused by mutations affecting the gene represented in this entry. Ref.16 Ref.23 Ref.27 Ref.31 Ref.38 Ref.39 Ref.42
Sequence similarities
Belongs to the glycosyl hydrolase 35 family.
