β-galactosidase
| Β-galactosidase | ||
|---|---|---|
|
||
| Beta-galactosidase tetramer, E. Coli according to PDB 3MV0 | ||
| Properties of human protein | ||
| Mass / length primary structure | 649 amino acids | |
| Isoforms | 2 | |
| Identifier | ||
| Gene names | GLB1 ; EBP; ELNR1; S-Gal | |
| External IDs | ||
| Drug information | ||
| ATC code | A16 AB04 | |
| DrugBank | DB00103 | |
| Enzyme classification | ||
| EC, category | 3.2.1.23 , glycosidase | |
| Response type | Hydrolysis of terminal β- D- galactose residues in β- D- galactosides | |
| Substrate | β- D- galactosides | |
| Products | β- D- galactose | |
| Occurrence | ||
| Homology family | Galactosidase 3 | |
| Parent taxon | Creature | |
β-galactosidases (also β-galactosidases ) are enzymes which hydrolytically split off terminal, glycosidically bound β- D - galactose from biomolecules (e.g. gangliosides , glycoproteins and glycosaminoglycans ). They occur in all living things where they have different roles in the metabolism. Bacterial β-galactosidase is used in the laboratory. Besides the bacterial lactase, which is also a β-galactosidase, there is also a human lactase that is not included in EC 3.2.1.23 . The human enzyme is encoded by the GLB1 gene in two splice variants that occur in all cells in both the lysosomes and the cytoplasm . Mutations in the GLB1 gene can lead to different types of gangliosidosis and to type 4B of mucopolysaccharidosis .
function
As exoglycosidases, they catalyze the hydrolysis of the glycosidic bond of β-galactopyranosides. This creates the monosaccharide galactose . β-galactosidases have different specificities depending on the task and organism; some of them can also hydrolyze α- L -arabinopyranosides.
use
In micro- and molecular biology , the gene for β-galactosidase, called lacZ , from the gram-negative bacterium Escherichia coli , is used as a reporter gene . In bacteria modified with genetic engineering (e.g. blue-white selection of colonies), yeasts (e.g. yeast two-hybrid system ) or even higher organisms (e.g. knockout mouse ) shows the hydrolysis of X-Gal (5-bromo-4-chloro-3-indoxyl-β- D- galactopyranoside) to galactose and a blue, water-insoluble indigo dye indicate the gene expression of lacZ .
The enzymatic activity of β-galactosidase is measured with the aid of the hydrolytic cleavage of ONPG ( o -nitrophenyl-β- D- galactopyranoside). Industrially, β-galactosidase is used intensively in the dairy industry, for example in the production of lactose-free milk or in the treatment of whey .
classification
β-galactosidases form family 35 in the Henrissat classification of glycosidases.
Individual evidence
- ↑ UniProt entry .
- ↑ Bernard Henrissat: Glycosyl hydrolase families: classification and list of entries .
