betagalactosidases

Beta-galactosidases are enzymes that catalyze the hydrolysis of beta-galactosides, most commonly lactose, into galactose and glucose. They belong to glycoside hydrolases and are designated by the enzyme commission number EC 3.2.1.23. These enzymes are found in a wide range of organisms, including bacteria, fungi, plants, and animals, and they play a central role in the metabolism of beta-galactosides. In bacteria such as Escherichia coli, the enzyme beta-galactosidase is encoded by the lacZ gene and enables utilization of lactose as a carbon source. In humans, lactose digestion is carried out by a related beta-galactosidase–type enzyme known as lactase, with other tissues expressing related enzymes that act on different substrates.

Structure and properties: Many beta-galactosidases are homotetramers, with subunits commonly around 100 kDa, though sizes vary by species. The catalytic mechanism involves acid-base chemistry at the active site to cleave the glycosidic bond. Activity and stability are influenced by pH and temperature and, in some cases, by the presence of metal ions, though this varies among enzymes from different sources.

Applications: In industry, beta-galactosidases are used to hydrolyze lactose in dairy processing, producing lactose-free products and enabling synthesis of galactooligosaccharides by transgalactosylation. In molecular biology, lacZ is a widely used reporter gene; substrates like X-gal yield a blue product upon cleavage, enabling blue-white screening. The enzymes also aid research into sugar metabolism and the production of complex galactosides.