B-galactosidase

β-Galactosidase

β-Galactosidase, also known as lactase, is an enzyme that catalyzes the hydrolysis of β-galactosides into monosaccharides. It is a crucial enzyme in the metabolism of lactose, a disaccharide sugar found in milk and dairy products. The enzyme is encoded by the lacZ gene in the lac operon of the bacterium *Escherichia coli* and is widely used in molecular biology as a reporter gene.

Structure

β-Galactosidase is a tetrameric protein composed of four identical subunits. Each subunit has a molecular weight of approximately 116 kDa. The enzyme's active site contains several key amino acids that are essential for its catalytic activity, including glutamic acid and aspartic acid residues that participate in the hydrolysis of the glycosidic bond.

Function

The primary function of β-galactosidase is to break down lactose into glucose and galactose, which can then be utilized by the organism for energy. This reaction is particularly important in organisms that consume milk as a primary source of nutrition. In humans, the enzyme is produced in the small intestine and is essential for the digestion of lactose in dairy products.

Clinical Significance

Deficiency in β-galactosidase activity in humans leads to lactose intolerance, a condition characterized by the inability to digest lactose, resulting in gastrointestinal symptoms such as bloating, diarrhea, and abdominal pain. Lactase supplements are available to aid those with lactose intolerance.

Applications in Molecular Biology

β-Galactosidase is widely used as a reporter gene in molecular biology experiments. The enzyme can cleave the synthetic substrate X-gal, producing a blue product that is easy to detect. This property is used in blue/white screening to identify recombinant bacteria in cloning experiments.

Also see

• Lactose intolerance
• Lac operon
• Enzyme kinetics
• Reporter gene