Background
Lactase is an enzyme produced in human digestive system which is essential to break down complex sugar lactose into simple sugar glucose and galactose. Lactase is also known as Lactase-phlorizin hydrolase (LPH), part of the β-galactosidase family of enzyme which is an integral protein of the intestinal brush-border membrane. This protein is encoded by lactase gene (LCT) in human and normally consists of more than 1000 amino acids within its structure and 1100kDA in its atomic mass. Two different phenotypes in adults which are commonly genetically determined polymorphism in the human population such as lactase persistent and lactase non-persistent. In order to digest large quantities of lactose from milk product, high level of lactase will be expressed in all healthy newborn children. The individuals without the expression of lactase will consequently become lactose intolerant with associated digestive problems. In contrast, lactase persistent individuals are able to break down and absorb the lactose with long life lactase expression.
General Lactase Information
- This enzyme found in lining of small intestine.
- Mostly produced in the cells (called enterocytes) of the villi.
- Acts as catalyst to breakdown lactose into glucose and galactose.
- Lactase promotes the hydrolysis of the Beta-D galactoside linkage of lactose.
- Low production of lactase will lead to lactose intolerance in human body.
- People who lacking lactase in their intestine can get abdominal cramps, flatulence and diarrhea when they consume milk product.
Mechanism of Lactase
- Figure 1 shows the molecular structure of lactose.
- Lactose is a disaccharide which is composed of glucose and galactose.
- Most of the polysaccharides and disaccharides must be digested to monosaccharides prior to absorption through the intestinal walls and into the bloodstream.
- The optimum temperature and optimum pH for lactase activity is about 77°F (25°C) and 6.0 to 6.5 respectively.
- Figure 3 shows the 3D structure of lactase.
- In metabolism, the β-1,4-glycosidic bond in D-lactose is hydrolyzed to form D-galactose and D-glucose.
- The overall reaction that lactase catalyzes is C12H22O11 + H2O → C6H12O6 + C6H12O6 + heat.
Function of Lactase
Figure 4: Lactase Enzyme (Source: http://www.1wallmart.com/product.php?id_product=552)
- Primary function of the lactase enzyme is to break down lactose, which is the milk sugar found in milk and milk related products into glucose and galactose.
- Both galactose and glucose are monosaccharides that are converted into energy for the body.
http://www.livestrong.com/article/390563-what-are-the-functions-
of-the-enzyme-lactase/)
Lactase-related Disease: Lactose Intolerance
Lactose intolerance is the body’s inability to properly digest lactose. This inability is due to a lack of lactase enzyme in the body. This lactase deficiency can lead to symptoms that include nausea, cramps, bloating, gas, and diarrhea. The severity of these symptoms varies depending on the amount of lactose each individual can tolerate. Lactose intolerance can be attributed to digestive diseases and injuries to the digestive system. The main cause of lactose intolerance is due to lactase deficiency that develops as the person ages.
Dairy products such as milk, ice cream and yogurt have high levels of lactose. These higher levels of lactose affect how much lactase your body requires for proper digestion. Curiously enough, yogurt does not trigger symptoms of lactose intolerance. This is primarily because bacterial cultures used to make yogurt produce some of the lactase, which breaks down the lactose for easy digestion ("General Lactase Information" from http://digestmilk.com/lactase.html).
Dairy products such as milk, ice cream and yogurt have high levels of lactose. These higher levels of lactose affect how much lactase your body requires for proper digestion. Curiously enough, yogurt does not trigger symptoms of lactose intolerance. This is primarily because bacterial cultures used to make yogurt produce some of the lactase, which breaks down the lactose for easy digestion ("General Lactase Information" from http://digestmilk.com/lactase.html).
Industrial Uses of Lactase
Lactase produced commercially can be extracted both from yeasts such as Kluyveromyces fragilis and Kluyveromyces lactis and from molds, such as Aspergillus niger and Aspergillus oryzae (Seyis and Aksoz, 2004).
1. Its primary commercial use is to break down lactose in milk to make it suitable for people with lactose intolerance (“Lactase” from http://www.diabetesdaily.com/wiki/Lactase).
1. Its primary commercial use is to break down lactose in milk to make it suitable for people with lactose intolerance (“Lactase” from http://www.diabetesdaily.com/wiki/Lactase).
2. It is also used in preparation of ice cream, to make a creamier and sweeter-tasting product (Philips, http://biotech.about.com/od/casestudies/a/dairyenzymes.htm).
3. For processing of whey that formed during cheese production: Lactase transforms the lactose in whey into a sweetish mixture of glucose and galactose. This product, after being refined and concentrated, becomes a syrup with a honey-like flavour. This syrup is used on a large scale in the industrial manufacture of sweets (''Lactase'' from http://www.gmo-compass.org/eng/database/enzymes/306.lactase.html).
4. Lactase is also used to screen for blue white colonies in the multiple cloning site (MCS) of various plasmid vectors in Escherichia coli or other bacteria (“Lactase” from http://www.diabetesdaily.com/wiki/Lactase).