Lactase (Lactase-phlorizin hydrolase) (LPH)

Lactase, also known as lactase-phlorizin hydrolase, is an enzyme primarily expressed in the brush border of intestinal epithelial cells in newborns, where it hydrolyzes the disaccharide lactose—abundant in mammalian milk—into its monosaccharide components, D-glucose and D-galactose. These products are then actively transported into cells via the sodium-glucose cotransporter SGLT1 (also called GLUT1 in some contexts) and further diffuse into the bloodstream via basolateral transporters like SLC2A2, ultimately reaching the liver for metabolism through glycolysis (glucose) or the Leloir pathway (galactose). Lactase activity naturally declines after weaning in most mammals, including many humans, leading to adult hypolactasia or lactose intolerance when undigested lactose ferments in the gut, causing bloating, diarrhea, and discomfort. While not a direct therapeutic target for drugs, lactase deficiency underlies lactose intolerance, managed symptomatically with lactase supplements or lactose-free diets rather than targeting the enzyme pharmacologically. In bacteria like E. coli, analogous lactose metabolism involves the lac operon (lacZ encoding β-galactosidase), but this is distinct from human lactase.

Other names

β-galactosidase (mammalian context)lactase-phlorizin hydrolaseintestinal lactase