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THE PHARMA REVIEW
(MARCH 2009) |
Lactase
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Piyush Rathi |
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Lactose intolerance is the inability to metabolize milk
sugar, or lactose. Lactose is a disaccharide found in
dairy products and is composed of glucose and galactose.
While lactose intolerance varies wildly from population
to population, scientists estimate that nearly 75% of
adults either lack the ability to digest lactose or at
least have difficulty digesting dairy products in
general. The frequency ranges from around 5% in northern
Europe to more than 90% in some Asian and African
countries.
The issue of whether we can digest lactose depends upon
the intestinal enzyme Lactase. Lactase (or
beta-galactosidase) is the enzyme that hydrolyzes
lactose into its component monosaccharides, galactose
and glucose. Lactase is naturally produced in the small
intestine. In the inner lumen of the small intestine,
projections called villi are covered with cells known as
enterocytes. These enterocytes are covered with a
membrane that has what is called a brush border. The
brush border is actually millions of microvilli and is
the site of lactase production.
Villi are projections into the lumen of the small
intestine that are covered with enterocytes. An electron
micrograph of the microvilli of an enterocyte with brush
border is shown
Lactase promotes the hydrolysis of the Beta-D
galactoside linkage of lactose, converting it into
D-glucose and D-galactose. This reaction provides two
positive results for dairy products, which we will cover
later in the article. Lactase is very active in the
duodenum. Its ability to handle lactose loads is very
closely related to the amount of lactose emptying from
the stomach into the duodenum. The optimum temperature
for lactase is about 48 °C (118.4 °F) for its activity
and has an optimum pH of 6.5.
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