- A disaccharide present in mammalian milk, occurring naturally as α- and β-l.; obtained from cow's milk and used in modified milk preparation, in food for infants and convalescents, and in pharmaceutical preparations; large doses act as an osmotic diuretic and as a laxative. Human milk contains 6.7% l.. SYN: milk sugar, saccharum lactis.- l. synthase the enzyme responsible for the synthesis of l., catalyzing the reaction between UDP-galactose and d-glucose to l. and UDP.
* * *lac·tose 'lak-.tōs, -.tōz n a disaccharide sugar C12H22O11 that is present in milk, yields glucose and galactose upon hydrolysis, yields esp. lactic acid upon fermentation, and is used chiefly in foods, medicines, and culture media (as for the manufacture of penicillin) called also milk sugar
* * *n.a sugar, consisting of one molecule of glucose and one of galactose, found only in milk. Lactose is split into its constituent sugars by the enzyme lactase, which is secreted in the small intestine. This enzyme is missing or is of low activity in certain people of some Eastern and African races. This leads to the inability to absorb lactose, known as lactose intolerance.
* * *lac·tose (lakґtōs) [L. lac, gen. lactis milk] a reducing disaccharide occurring as the D-isomer, in both α- and β-configurations, as a major constituent of mammalian milk; on hydrolysis by acids or intestinal lactase, it forms one residue each of galactose and glucose. Cf. lactose intolerance, under intolerance. Lactose is used as a tablet and capsule diluent, a powder bulking agent, in infant feeding formulas, and as a nutritional supplement.
Medical dictionary. 2011.