BetaDgalactosides

betaDgalactosides are a class of disaccharides that contain a galactose sugar unit linked via a beta glycosidic bond. The most common and well-known betaDgalactoside is lactose, also known as milk sugar. Lactose is composed of galactose and glucose units joined by a beta1-4 glycosidic linkage. Other examples include melibiose, which consists of galactose and glucose linked by an alpha1-6 bond, and its isomer, gentiobiose, which has a beta1-6 linkage. These compounds are important in biological systems. For instance, lactose is a primary carbohydrate source in the milk of mammals and is broken down into its constituent monosaccharides, glucose and galactose, by the enzyme lactase during digestion. The presence or absence of lactase activity in individuals leads to lactose intolerance. BetaDgalactosides also play roles in cell recognition and as components of more complex glycoconjugates.