betaDgalactose

Beta-D-galactose, commonly written as β-D-galactose, is the beta anomer of the aldohexose D-galactose. It has the molecular formula C6H12O6 and is a monosaccharide. In its preferred cyclic form, it exists as beta-D-galactopyranose, a six-membered ring in which the anomeric hydroxyl group on carbon 1 is oriented equatorially (beta) and the sugar displays the D-configuration at the stereogenic carbon C5. In solution, alpha and beta anomers interconvert through mutarotation, with the beta form often being more stable under typical conditions.

Beta-D-galactose is a natural component of lactose, the disaccharide found in milk, where it is linked to glucose via a β-1,4-glycosidic bond. It also occurs in free form in trace amounts in various foods and is a metabolic intermediate in animals and microbes. In metabolism, galactose is processed through the Leloir pathway: galactokinase converts galactose to galactose-1-phosphate, which is then converted by galactose-1-phosphate uridylyltransferase to UDP-galactose; UDP-galactose can be epimerized to UDP-glucose. UDP-galactose serves as a donor for galactosylation reactions in the biosynthesis of glycoproteins, glycolipids, and lactose.

Defects in galactose metabolism, such as GALT deficiency, cause galactosemia, a metabolic disorder. Thus, beta-D-galactose has both dietary significance and an essential role as a metabolic intermediate in biosynthetic pathways.