15 by: Ainsley Barisoff
Student: Ainsley Barisoff
Enzyme name: Beta-galactosidase
E.C. number: 3.2.1.23
Where is beta-galactosidase found? Beta-galactosidase is found in the small intestine of mammals. It is also present and functional in bacteria, fungi, plants, and yeast.
What does beta-galactosidase do? Beta-galactosidase catalyzes the hydrolysis of lactose (a disaccharide) into D-glucose and D-galactose (monosaccharides). Other functions include catalysis of lactose to allolactose and cleavage of allolactose back to monosaccharides. In this project, the hydrolysis of galactose is the mechanism of interest. Hydrolysis of lactose occurs in two mechanistic steps, galactosylation, and degalactosylation. Before hydrolysis can occur, lactose binds to the active site in shallow mode. A rotation of the substrate occurs to move it to the deep site. In Galactosylation, Glu537 acts as a nucleophile and Glu461 as a proton donor. This allows the glucose portion of lactose to dissociate and the galactose portion to covalently bond to Glu537. In step two, a water molecule accepts the galactose, releasing it from the active site.
Interesting facts
- When beta-galactosidase reacts with X-gal (galactose compound that has no colour), a bright blue colour is produced. This happens due to the indole component of X-gal that dissociates when the enzyme binds to and hydrolyzes the galactose containing molecule.
- Lactose intolerance is caused by a lack of beta-galactosidase in the small intestine. Affected individuals are unable to digest lactose. Once lactose arrives in the large intestine, un-hydrolyzed, it is fermented leading to symptoms of lactose intolerance.
References
Beta-galactosidase. Mechanism and Catalytic Site Atlas. EMBL-EBI. https://www.ebi.ac.uk/thornton-srv/m-csa/entry/422/
Juers, D. H., Matthews, B. W., Huber, R. E. (2012). LacZβ-galactosidase: Structure and function of an enzyme of historical and molecular biological importance. Protein Science, 21, 1792-1807. https://doi.org/10.1002/pro.2165
Kalathinathan, P., Sain, A., Pulicherla, K., Muthukaliannan, G. K., (2023). A Review on the Various Sources of β-Galactosidase and Its Lactose Hydrolysis Property . Current Microbiology, 80 (122). https://doi.org/10.1007/s00284-023-03220-4
