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Lactase (LCT), a member of the β-galactosidase family of enzyme, is involved in the hydrolysis of the disaccharide lactose into constituent galactose and glucose monomers. In humans, lactase is present predominantly along the brush border membrane of the differentiated enterocytes lining the villi of the small intestine.
Lactase is essential for digestive hydrolysis of lactose in milk. Deficiency of the enzyme causes lactose intolerance; most humans become lactose intolerant as adults.
Characteristics
Lactase has an optimum temperature of about 48 °C for its activity and an optimum pH of 6.5. In humans, the gene is localised on the second chromosome (2q21). Bacterial and Archaea lactase lack a membrane binding domain and free float around the cell, these also tend to be more general β-galactosidase that will cleave more then just lactose.
Gene
Lactase persistence, the genetic trait in which intestinal lactase activity persists at childhood levels into adulthood, varies in frequency in different human populations, being most frequent in northern Europeans and certain African and Arabian nomadic tribes, who have a history of drinking fresh milk.
Lactase persistence is not due to mutations within the lactase gene, LCT, but to mutations outside the gene in control regions that regulate its expression. They are two intronic variations (C/T and G/A) in the MCM6 gene, MCM6, located approximately 14 kb (-13910) and 22 kb (-22018) upstream of LCT, respectively.Identification of a variant associated with adult-type hypolactasia. Nat Genet 2002;30: 233-7. Free text. PMID 11788828. C/T(-13910) variant has been shown that can function in vitro as a cis element capable of enhancing differential transcriptional activation of LCT promoter.Olds LC, Sibley E. Lactase persistence DNA variant enhances lactase promoter activity in vitro: functional role as a cis regulatory element. Hum Mol Genet 2003 Sep 15; 12(18): 2333-40.'' Free text. PMID 12915462.
Industrial use
Lactase produced commercially can be extracted both from yeasts such as Kluyveromyces fragilis and Kluyveromyces lactis and from fungi, such as Aspergillus niger and Aspergillus oryzae.Seyis I, Aksoz N. Production of lactase by Trichoderma sp.. Food Technol Biotechnol 2004;42:121–124. Free text. Its primary commercial use is to break down lactose in milk to make it suitable for people with lactose intolerance. Lactase is also used in the manufacture of ice cream. Because glucose and galactose are sweeter than lactose, lactase produces a more pleasant taste. Lactose also crystallises at the low temperatures of ice cream; however, its constituent products stay liquid and contribute to a smoother texture. Lactase is used in the conversion of whey into syrup.
Also used to screen for blue white colonies into the MCS of various plasmid vectors in E.Coli or other bacteria, as the lacZ gene is destroyed
External links
- E. coli β-galactosidase:
- The use of lactases in the dairy industry
References
Laktase | Lactase | Laktazo | לקטאז | Lactase | Laktaza | Lactase | Laktaasi
"Lactase"