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Lactase persistence or lactose tolerance is the continued activity of the lactase enzyme in adulthood, allowing the digestion of lactose in milk. In most mammals , the activity of the enzyme is dramatically reduced after weaning . [ 1 ]
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. Lactase is found in the brush border of the small intestine of humans and other mammals.
In the milk of most mammals, lactose is generally the major carbohydrate, so when you have a glass of milk, and it gets through your stomach to the small intestine, that lactose gets chopped into glucose and galactose by an enzyme that’s fittingly called lactase. The gene responsible for production of the lactase enzyme is expressed ...
Lactose, or milk sugar, is a disaccharide composed of galactose and glucose and has the molecular formula C 12 H 22 O 11. Lactose makes up around 2–8% of milk (by mass). The name comes from lact (gen. lactis ), the Latin word for milk, plus the suffix -ose used to name sugars.
Primary hypolactasia, or primary lactase deficiency, is genetic, develops in childhood at various ages, and is caused by the absence of a lactase persistence allele. In individuals without the lactase persistence allele, less lactase is produced by the body over time, leading to hypolactasia in adulthood.
Galactose (/ ɡ ə ˈ l æ k t oʊ s /, galacto-+ -ose, "milk sugar"), sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweet as glucose, and about 65% as sweet as sucrose. [2] It is an aldohexose and a C-4 epimer of glucose. [3] A galactose molecule linked with a glucose molecule forms a lactose molecule.
Alpha-lactalbumin, which is expressed in response to prolactin, increases the affinity of N-acetyllactosamine synthase for its substrate, causing increased production of lactose during lactation. The interaction that facilitates lactose biosynthesis consists of a-lactalbumin (the regulatory unit) binding reversibly to the glycosyltransferase.
In most mammals, production of lactase diminishes after infants are weaned from maternal milk. However, 5% to 90% of the human population possess an advantageous autosomal mutation in which lactase production persists after infancy. The geographic distribution of lactase persistence is concordant with areas of high milk intake.