Lactase

LCT
Identifiers
Aliases	LCT, LAC, LPH, LPH1, lactase
External IDs	OMIM: 603202; MGI: 104576; GeneCards: LCT
Enzyme activity
Gene location (Human)
Chr.	Chromosome 2 (human)
End	135,837,184 bp
Gene location (Mouse)
Chr.	Chromosome 1 (mouse)
End	128,256,055 bp
RNA expression pattern
	Top expressed in
	jejunal mucosa; ; duodenum; ; mucosa of ileum; ; appendix; ; gonad; ; lymph node; ; liver; ; kidney; ; blood; ; hippocampal formation;
	Top expressed in
	duodenum; ; migratory enteric neural crest cell; ; epithelium of small intestine; ; jejunum; ; intestinal villus; ; lumbar spinal ganglion; ; dentate gyrus; ; Ileal epithelium; ; sexually immature organism; ; hippocampus proper;
	More reference expression data
	n/a
Gene ontology
Molecular function	hydrolase activity, hydrolyzing O-glycosyl compounds; hydrolase activity, acting on glycosyl bonds; catalytic activity; glycosylceramidase activity; hydrolase activity; beta-glucosidase activity; lactase activity;
Cellular component	integral component of membrane; membrane; plasma membrane; integral component of plasma membrane; apical plasma membrane;
Biological process	polysaccharide digestion; metabolism; glycosyl compound metabolic process; carbohydrate metabolic process;
	Sources:Amigo / QuickGO
Orthologs
Databases	NCBI: entry; OMA: entry
	3938
	226413
	ENSG00000115850
	ENSMUSG00000026354
	P09848
	F8VPT3
	NM_002299
	NM_001081078
	NP_002290
	NP_001074547
	Wikidata
View/Edit Human	View/Edit Mouse

Search
PMC	articles
PubMed	articles
NCBI	proteins

Lactase
Lactase
	E. coli lactase tetramer. PDB: 1JYN
Identifiers
EC no.	3.2.1.108
CAS no.	9031-11-2
Databases
BRENDA	enzyme data
ExPASy	NiceZyme view
KEGG	enzyme entry
MetaCyc	metabolic pathway
Rhea	reactions
PDB structures	RCSB PDB PDBe PDBsum
Gene Ontology	AmiGO / QuickGO
PMC
Search
PMC	articles
PubMed	articles
NCBI	proteins

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:

2D representation of the chemical structure of Q56229948.

lactose

H₂O

Rightward reaction arrow with minor substrate(s) from top left

2D representation of the chemical structure of Q27103248.

β-D-galactose

+

2D representation of the chemical structure of Q23905964.

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. Lactase is found in the brush border of the small intestine of humans and other mammals. People without the mutation allowing production of functional LCT to continue past infancy may experience the symptoms of lactose intolerance after consuming milk products.

Microbial β-galactosidases that can hydrolyze lactose (i.e. a lactase in the broader sense) 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.