Lactase

See Lactose intolerance

Lactase is an enzyme located in the brush border of the small intestine of humans.

It consists of a single 160-kDa polypeptide chain that localizes to the brush border membrane of intestinal epithelial cells.

It is essential to the complete digestion of whole milk; it breaks down lactose, a sugar which gives milk its sweetness.

Lacking lactase, one may experience the symptoms of lactose intolerance when consuming dairy products.

Lactase can be purchased as a food supplement, and is added to milk to produce lactose-free milk products.

It reaches its highest levels in the human small intestine after birth and then begins a slow decline unless milk is consumed regularly.

It is a glycoside hydrolase involved in the hydrolysis of the disaccharide lactose into constituent galactose and glucose monomers.

It is present predominantly along the brush border membrane of the differentiated enterocytes lining the villi of the small intestine, and is encoded by the LCT gene.

Some people are unable to produce it in their small intestine, and cannot break down the natural lactose in milk, leaving them with diarrhea, gas and bloating when drinking regular milk.

Without lactase, lactose intolerant people pass lactose undigested to the colon where bacteria break it down, creating carbon dioxide and that leads to bloating and flatulence.

Lactase supplements are used to treat lactose intolerance.

It is encoded by a single genetic locus on chromosome 2.

Neonates are born with high levels of lactase expression.

Lactase transcription is down-regulated after weaning, resulting in diminished lactase expression in the small intestine.

Some population segments exhibit lactase persistence due to a mutation.

This mutation has allowed almost half of the world’s population to metabolize lactose without symptoms.

There is a link in the the occurrence of lactase persistence to two different single-nucleotide polymorphisms in the LPH gene.

Little difference exists in lactase expression in infants, indicating that the mutations become increasingly relevant during development.