Lactase
| Lactase | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| EC no. | 3.2.1.108 | ||||||||
| CAS no. | 9031-11-2 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
| Gene Ontology | AmiGO / QuickGO | ||||||||
| |||||||||
| Lactase | |||||||
|---|---|---|---|---|---|---|---|
| Identifiers | |||||||
| Symbol | LCT | ||||||
| Alt. symbols | LAC; LPH; LPH1 | ||||||
| NCBI gene | 3938 | ||||||
| HGNC | 6530 | ||||||
| OMIM | 603202 | ||||||
| RefSeq | NM_002299 | ||||||
| UniProt | P09848 | ||||||
| Other data | |||||||
| EC number | 3.2.1.108 | ||||||
| Locus | Chr. 2 q21 | ||||||
| |||||||
Lactase (EC 3.2.1.108) is an enzyme produced by many organisms and is essential to the complete digestion of whole milk. It breaks down the sugar lactose into its component parts, galactose and glucose, simple sugars that can be absorbed into the bloodstream through an animal's intestines. A lactase is a type of β-galactosidase because it breaks down the β-glycosidic bond in D-lactose. The chemical reaction it catalyzes is:
- C12H22O11 + H2O → C6H12O6 + C6H12O6 + heat.
- lactose + H2O → β-D-galactose + D-glucose
The only human gene encoding a lactase is LCT or lactase-phlorizin hydrolase (alternative symbol LPH). LCT has a lactase domain and a phlorizin hydrolase domain. It is encoded on chromosome 2.[1][2] Lactase is found in the brush border of the small intestine of humans and other mammals. People deficient in LCT or lacking functional LCT may experience the symptoms of lactose intolerance after consuming milk products.[3]
Microbial β-galactosidases that can hydrolyze lactose (i.e. a lactase in the broader sense)[a] can be purchased as a food supplement and is added to milk to produce "lactose-free" milk products. This enzyme can directly break down lactose when added to dairy. Some versions can survive passage through the human stomach and break down lactose in any ingested food before it reaches the colon.
- ^ Mantei N, Villa M, Enzler T, Wacker H, Boll W, James P, Hunziker W, Semenza G (Sep 1988). "Complete primary structure of human and rabbit lactase-phlorizin hydrolase: implications for biosynthesis, membrane anchoring and evolution of the enzyme". The EMBO Journal. 7 (9): 2705–13. doi:10.1002/j.1460-2075.1988.tb03124.x. PMC 457059. PMID 2460343.
- ^ Harvey CB, Fox MF, Jeggo PA, Mantei N, Povey S, Swallow DM (Jul 1993). "Regional localization of the lactase-phlorizin hydrolase gene, LCT, to chromosome 2q21". Annals of Human Genetics. 57 (Pt 3): 179–85. doi:10.1111/j.1469-1809.1993.tb01593.x. PMID 8257087. S2CID 38604778.
- ^ Järvelä I, Torniainen S, Kolho KL (2009). "Molecular genetics of human lactase deficiencies". Annals of Medicine. 41 (8): 568–75. doi:10.1080/07853890903121033. PMID 19639477. S2CID 205586720.
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