α-Amylase is a protein enzyme EC 3.2.1.1 that hydrolyses alpha bonds of large,
alpha-linked polysaccharides, such as starch and glycogen, yielding glucose
and maltose. It is the major form of amylase found in humans and other
mammals. It is also present in seeds containing starch as a food reserve, and
is secreted by many fungi. In human physiology
Although found in many tissues, amylase is most prominent in pancreatic juice
and saliva, each of which has its own isoform of human α-amylase. They behave
differently on isoelectric focusing, and can also be separated in testing by
using specific monoclonal antibodies. In humans, all amylase isoforms link to
chromosome 1p21. = Salivary amylase =
Amylase is found in saliva and breaks starch into maltose and dextrin. This
form of amylase is also called "ptyalin" It will break large, insoluble starch
molecules into soluble starches producing successively smaller starches
and ultimately maltose. Ptyalin acts on linear α(1,4) glycosidic linkages, but
compound hydrolysis requires an enzyme that acts on branched products. Salivary
amylase is inactivated in the stomach by gastric acid. In gastric juice adjusted
to pH 3.3, ptyalin was totally inactivated in 20 minutes at 37°C. In
contrast, 50% of amylase activity remained after 150 minutes of exposure
to gastric juice at pH 4.3. Both starch, the substrate for ptyalin, and the
product are able to partially protect it against inactivation by gastric acid.
Ptyalin added to buffer at pH 3.0 underwent complete inactivation in 120
minutes; however, addition of starch at a 0.1% level resulted in 10% of the
activity remaining, and similar addition of starch to a 1.0% level resulted in
about 40% of the activity remaining at 120 minutes.
Optimum conditions for ptyalin Optimum pH - 7.0
Human body temperature Presence of certain anions and
activators: Chloride and bromide – most effective
Iodide – less effective Sulfate and phosphate – least effective
= Genetic variation in human salivary amylase =
The salivary amylase gene has undergone duplication during evolution, and DNA
hybridization studies indicate many individuals have multiple tandem repeats
of the gene. The number of gene copies correlates with the levels of salivary
amylase, as measured by protein blot assays using antibodies to human
amylase. Gene copy number is associated with apparent evolutionary exposure to
high-starch diets. For example, a Japanese individual had 14 copies of the
amylase gene. The Japanese diet has traditionally contained large amounts of
rice starch. In contrast, a Biaka individual carried six copies. The Biaka
are rainforest hunter-gatherers who have traditionally consumed a low-starch
diet. Perry and colleagues speculated the increased copy number of the
salivary amylase gene may have enhanced survival coincident to a shift to a
starchy diet during human evolution. Pancreatic amylase
Pancreatic α-amylase randomly cleaves the α(1-4) glycosidic linkages of
amylose to yield dextrin, maltose, or maltotriose. It adopts a double
displacement mechanism with retention of anomeric configuration.
= In pathology = The test for amylase is easier to
perform than that for lipase, making it the primary test used to detect and
monitor pancreatitis. Medical laboratories will usually measure either
pancreatic amylase or total amylase. If only pancreatic amylase is measured, an
increase will not be noted with mumps or other salivary gland trauma.
However, because of the small amount present, timing is critical when
sampling blood for this measurement. Blood should be taken soon after a bout
of pancreatitis pain, otherwise it is excreted rapidly by the kidneys.
Salivary α-amylase has been used as a biomarker for stress that does not
require a blood draw. Interpretation
Increased plasma levels in humans are found in:
Salivary trauma Mumps — due to inflammation of the
salivary glands Pancreatitis — because of damage to the
cells that produce amylase Renal failure — due to reduced excretion
Total amylase readings of over 10 times the upper limit of normal are suggestive
of pancreatitis. Five to 10 times the ULN may indicate ileus or duodenal
disease or renal failure, and lower elevations are commonly found in
salivary gland disease. = Genes =
salivary - AMY1A, AMY1B, AMY1C pancreatic - AMY2A, AMY2B
In grain α-Amylase activity in grain is measured
by, for instance, the Hagberg-Perten Falling Number, a test to assess sprout
damages, or the Phadebas method. Industrial use
α-Amylase is used in ethanol production to break starches in grains into
fermentable sugars. The first step in the production of
high-fructose corn syrup is the treatment of cornstarch with α-amylase,
producing shorter chains of sugars oligosaccharides.
An α-amylase called "Termamyl", sourced from Bacillus licheniformis, is also
used in some detergents, especially dishwashing and starch-removing
detergents. See amylase for more uses of the amylase
family in general. Buffer inhibition
The tris molecule is reported to inhibit a number of bacterial α-amylases, so
they should not be used in tris buffer. Determination
Several methods are available for determination of α-amylase activity, and
different industries tend to rely on different methods. The starch iodine
test, a development of the iodine test, is based on colour change, as α-amylase
degrades starch and is commonly used in many applications. A similar but
industrially produced test is the Phadebas amylase test, which is used as
a qualitative and quantitative test within many industries, such as
detergents, various flour, grain, and malt foods, and forensic biology.
Domain architecture α-Amylases contain a number of distinct
protein domains. The catalytic domain has a structure consisting of an
eight-stranded alpha/beta barrel that contains the active site, interrupted by
a ~70-amino acid calcium-binding domain protruding between beta strand 3 and
alpha helix 3, and a carboxyl-terminal Greek key beta-barrel domain. Several
alpha-amylases contain a beta-sheet domain, usually at the C terminus. This
domain is organised as a five-stranded antiparallel beta-sheet. Several
alpha-amylases contain an all-beta domain, usually at the C terminus.
See also Digestive enzyme
References External links
The alpha-Amylase Protein alpha-Amylase at the US National Library
of Medicine Medical Subject Headings This article incorporates text from the
public domain Pfam and InterPro IPR006047 This article incorporates text
from the public domain Pfam and InterPro IPR012850 This article incorporates text
from the public domain Pfam and InterPro IPR006048