Amylase is an enzyme that catalyses the hydrolysis of starch into sugars.
Amylase is present in the saliva of humans and some other mammals, where it begins the
chemical process of digestion.
Foods that contain large amounts of starch but little sugar, such as rice and potatoes,
may acquire a slightly sweet taste as they are chewed because amylase degrades some of
their starch into sugar.
The pancreas and salivary gland make amylase to hydrolyse dietary starch into disaccharides
and trisaccharides which are converted by other enzymes to glucose to supply the body
with energy.
Plants and some bacteria also produce amylase.
As diastase, amylase was the first enzyme to be discovered and isolated.
Specific amylase proteins are designated by different Greek letters.
All amylases are glycoside hydrolases and act on α-1,4-glycosidic bonds.
Classification α-Amylase
The α-amylases are calcium metalloenzymes, completely unable to function in the absence
of calcium.
By acting at random locations along the starch chain, α-amylase breaks down long-chain carbohydrates,
ultimately yielding maltotriose and maltose from amylose, or maltose, glucose and "limit
dextrin" from amylopectin.
Because it can act anywhere on the substrate, α-amylase tends to be faster-acting than
β-amylase.
In animals, it is a major digestive enzyme, and its optimum pH is 6.7–7.0.
In human physiology, both the salivary and pancreatic amylases are α-amylases.
The α-amylases form is also found in plants, fungi and bacteria
β-Amylase Another form of amylase, β-amylase is also
synthesized by bacteria, fungi, and plants.
Working from the non-reducing end, β-amylase catalyzes the hydrolysis of the second α-1,4
glycosidic bond, cleaving off two glucose units at a time.
During the ripening of fruit, β-amylase breaks starch into maltose, resulting in the sweet
flavor of ripe fruit.
Both α-amylase and β-amylase are present in seeds; β-amylase is present in an inactive
form prior to germination, whereas α-amylase and proteases appear once germination has
begun.
Many microbes also produce amylase to degrade extracellular starches.
Animal tissues do not contain β-amylase, although it may be present in microorganisms
contained within the digestive tract.
The optimum pH for β-amylase is 4.0–5.0 γ-Amylase
γ-Amylase will cleave α(1–6) glycosidic linkages, as well as the last α(1–4)glycosidic
linkages at the nonreducing end of amylose and amylopectin, yielding glucose.
The γ-amylase has most acidic optimum pH of all amylases because it is most active
around pH 3.
Uses Fermentation
Alpha and beta amylases are important in brewing beer and liquor made from sugars derived from
starch.
In fermentation, yeast ingest sugars and excrete alcohol.
In beer and some liquors, the sugars present at the beginning of fermentation have been
produced by "mashing" grains or other starch sources.
In traditional beer brewing, malted barley is mixed with hot water to create a "mash,"
which is held at a given temperature to allow the amylases in the malted grain to convert
the barley's starch into sugars.
Different temperatures optimize the activity of alpha or beta amylase, resulting in different
mixtures of fermentable and unfermentable sugars.
In selecting mash temperature and grain-to-water ratio, a brewer can change the alcohol content,
mouthfeel, aroma, and flavor of the finished beer.
In some historic methods of producing alcoholic beverages, the conversion of starch to sugar
starts with the brewer chewing grain to mix it with saliva.
This practice is no longer in general use.
Flour additive Amylases are used in breadmaking and to break
down complex sugars, such as starch, into simple sugars.
Yeast then feeds on these simple sugars and converts it into the waste products of alcohol
and CO2.
This imparts flavour and causes the bread to rise.
While amylases are found naturally in yeast cells, it takes time for the yeast to produce
enough of these enzymes to break down significant quantities of starch in the bread.
This is the reason for long fermented doughs such as sour dough.
Modern breadmaking techniques have included amylases into bread improver, thereby making
the process faster and more practical for commercial use.
Alpha amylase is often listed as an ingredient on commercially package milled flour.
Bakers with long exposure to amylase-enriched flour are at risk of developing dermatitis
or asthma.
Molecular biology In molecular biology, the presence of amylase
can serve as an additional method of selecting for successful integration of a reporter construct
in addition to antibiotic resistance.
As reporter genes are flanked by homologous regions of the structural gene for amylase,
successful integration will disrupt the amylase gene and prevent starch degradation, which
is easily detectable through iodine staining.
Other uses An inhibitor of alpha-amylase, called phaseolamin,
has been tested as a potential diet aid.
When used as a food additive, amylase has E number E1100, and may be derived from swine
pancreas or mould mushroom.
Bacilliary amylase is also used in clothing and dishwasher detergents to dissolve starches
from fabrics and dishes.
Factory workers who work with amylase for any of the above uses are at increased risk
of occupational asthma.
Five to nine percent of bakers have a positive skin test, and a fourth to a third of bakers
with breathing problems are hypersensitive to amylase.
Hyperamylasemia Blood serum amylase may be measured for purposes
of medical diagnosis.
A higher than normal concentration may reflect one of several medical conditions, including
acute inflammation of the pancreas, but also perforated peptic ulcer, torsion of an ovarian
cyst, strangulation ileus, mesenteric ischemia, macroamylasemia and mumps.
Amylase may be measured in other body fluids, including urine and peritoneal fluid.
A January 2007 study from Washington University in St. Louis suggests that saliva tests of
the enzyme could be used to indicate sleep deficits, as the enzyme increases its activity
in correlation with the length of time a subject has been deprived of sleep.
History In 1831, Erhard Friedrich Leuchs described
the hydrolysis of starch by saliva, due to the presence of an enzyme in saliva, "ptyalin",
an amylase.
The modern history of enzymes began in 1833, when French chemists Anselme Payen and Jean-François
Persoz isolated an amylase complex from germinating barley and named it "diastase".
In 1862, Alexander Jakulowitsch Danilewsky separated pancreatic amylase from trypsin.
Human evolution Carbohydrates are a food source rich in energy.
Amylase is thought to have played a key role in human evolution in allowing humans an alternative
to fruit and protein.
A duplication of the pancreatic amylase gene developed independently in humans and rodents,
which could be suggestive of the importance of the gene.
The salivary amylase levels found in the human lineage are six to eight times higher in humans
than in chimpanzees, which are mostly fruit eaters and ingest little starch relative to
humans.
References
External links Molecule of the month February 2006 at the
Protein Data Bank.
Nutrition Sciences 101 at University of Arizona.
Amylase at Lab Tests Online.
Amylase: analyte monograph – The Association for Clinical Biochemistry and Laboratory Medicine.