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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.
The molecular structure of α-lactose, as determined by X-ray crystallography. Lactose crystals, viewed under polarized light. Lactose is a disaccharide composed of galactose and glucose, which form a β-1→4 glycosidic linkage. Its systematic name is β-D-galactopyranosyl-(1→4)-D-glucose.
This is an accepted version of this page This is the latest accepted revision, reviewed on 18 December 2024. Sweet-tasting, water-soluble carbohydrates This article is about the class of sweet-flavored substances used as food. For common table sugar, see Sucrose. For other uses, see Sugar (disambiguation). Sugars (clockwise from top-left): white refined, unrefined, unprocessed cane, brown ...
GalT encodes for the protein galactosyltransferase which catalyzes the transfer of a galactose sugar to an acceptor, forming a glycosidic bond. [5] GalK encodes for a kinase that phosphorylates α-D-galactose to galactose 1-phosphate. [6] Lastly, galM catalyzes the conversion of β-D-galactose to α-D-galactose as the first step in galactose ...
The lactose operon (lac operon) is an operon required for the transport and metabolism of lactose in E. coli and many other enteric bacteria.Although glucose is the preferred carbon source for most enteric bacteria, the lac operon allows for the effective digestion of lactose when glucose is not available through the activity of β-galactosidase. [1]
β-Galactosidase (EC 3.2.1.23, beta-gal or β-gal; systematic name β-D-galactoside galactohydrolase) is a glycoside hydrolase enzyme that catalyzes hydrolysis of terminal non-reducing β-D-galactose residues in β-D-galactosides. (This enzyme digests many β-Galactosides, not just lactose.
Cartoon diagram of a dimer of Escherichia coli galactose-1-phosphate uridylyltransferase (GALT) in complex with UDP-galactose (stick models). Potassium, zinc, and iron ions are visible as purple, gray, and bronze-colored spheres respectively.
First, Asp-170 performs a nucleophilic attack on the glycosidic bond to release the terminal α-galactose molecule from the ligand. Then, Asp-231 serves as an acid to remove a proton from water, making it more nucleophilic to attack the galactose-Asp complex and release α-galactose from the active site. [3] [4] [5]