Betagalactosidase

Beta-galactosidase is a hydrolytic enzyme that catalyzes the hydrolysis of beta-galactosides, including lactose, into their component sugars. In bacteria such as Escherichia coli, the enzyme is encoded by the lacZ gene and is a key component of the lactose operon (lacZYA). The enzyme is widely studied as a model system in molecular biology and is used as a reporter to monitor gene expression and promoter activity.

Chemically, beta-galactosidase acts on beta-galactosides by cleaving the glycosidic bond, producing glucose or galactose as products. The E. coli version operates via a retaining mechanism in which a covalent galactosyl-enzyme intermediate is formed during catalysis. The enzyme has a broad substrate range, including synthetic substrates such as o-nitrophenyl-β-D-galactopyranoside (ONPG), which is used in colorimetric assays, and chromogenic substrates such as X-gal for blue-white screening.

Structurally, beta-galactosidase is a tetramer, with each subunit contributing to a total molecular mass of roughly 450–470 kDa. Each subunit is about 100 kDa in size and contains the catalytic core necessary for bond cleavage. The LacZ enzyme is commonly studied alongside LacY and LacA within the lac operon, whose expression is regulated by the lac repressor and is induced by lactose or allolactose and modulated by glucose through catabolite repression.

Applications include blue-white screening in cloning experiments, enzymatic assays using ONPG, and industrial processes to reduce lactose content in dairy products. Variants and homologs exist across species, reflecting adaptations to different cellular environments.