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A diagram of an amylase molecule from human saliva. Calcium ion visible in pale khaki; chloride ion in green. From PDB 1SMD.
Human pancreatic amylase. Calcium ion visible in pale khaki; chloride ion in green. From PDB 1HNY.

Amylase is an enzyme that breaks starch down into sugar. Amylase is present in human saliva, where it begins the chemical process of digestion. Foods that contain much starch but little sugar, such as rice and potato, taste slightly sweet as they are chewed because amylase turns some of their starch into sugar in the mouth. The pancreas also makes amylase (alpha 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 (by Anselme Payen in 1833).[citation needed] Specific amylase proteins are designated by different Greek letters. All amylases are glycoside hydrolases and act on α-1,4-glycosidic bonds. It will start to denature at around 60C.

Contents

Classification

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α-Amylase

(EC 3.2.1.1 ) (CAS# 9014-71-5) (alternate names: 1,4-α-D-glucan glucanohydrolase; glycogenase) 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. [1]

In human physiology, both the salivary and pancreatic amylases hi its meα-Amylases. They are discussed in much more detail at alpha-Amylase.

Also found in plants (adequately), fungi (ascomycetes and basidiomycetes) and bacteria (Bacillus).

β-Amylase

(EC 3.2.1.2 ) (alternate names: 1,4-α-D-glucan maltohydrolase; glycogenase; saccharogen 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 (maltose) 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. Cereal grain amylase is key to the production of malt. Many microbes also produce amylase to degrade extracellular starches. Animal tissues do not contain β-amylase, although it may be present in microrganisms contained within the digestive tract.

γ-Amylase

(EC 3.2.1.3 ) (alternative names: Glucan 1,4-α-glucosidase; amyloglucosidase; Exo-1,4-α-glucosidase; glucoamylase; lysosomal α-glucosidase; 1,4-α-D-glucan glucohydrolase) In addition to cleaving the last α(1-4)glycosidic linkages at the nonreducing end of amylose and amylopectin, yielding glucose, γ-amylase will cleave α(1-6) glycosidic linkages. Unlike the other forms of amylase, γ-amylase is most efficient in acidic environments and has an optimum pH of 3.

Uses

Amylase enzymes finds use in bread making and to break down complex sugars such as starch (found in flour) 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 Amylase enzymes 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 bread making techniques have included amylase enzymes (often in the form of malted barley) into bread improver thereby making the bread making process faster and more practical for commercial use.[2]

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.

Workers in factories that work with amylase for any of the above uses are at increased risk of occupational asthma. 5-9% of bakers have a positive skin test, and a fourth to a third of bakers with breathing problems are hypersensitive to amylase. [3]

An inhibitor of alpha-amylase called phaseolamin has been tested as a potential diet aid. [4]

Blood serum amylase may be measured for purposes of medical diagnosis. A normal concentration is in the range 21-101 U/L. A higher than normal concentration may reflect one of several medical conditions, including acute inflammation of the pancreas, macroamylasemia, perforated peptic ulcer, and mumps. Amylase may be measured in other body fluids, including urine and peritoneal fluid.

History

In 1831 Erhard Friedrich Leuchs (1800-1837) described the diastatic action of salivary ptyalin (amylase) on starch.[5] The modern history of enzymes began in 1833 when French chemists described the isolation of an amylase complex from germinating barley and named it diastase.[6] In 1862 Danielewski separated pancreatic amylase from trypsin.[7]

Human evolution

Carbohydrates are an energy rich food source. 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, further suggesting its importance. 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. [8]

References

  1. ^ Effects of pH (Introduction to Enzymes)
  2. ^ Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1. 
  3. ^ Mapp CE (May 2001). "Agents, old and new, causing occupational asthma". Occup Environ Med 58 (5): 354–60, 290. doi:10.1136/oem.58.5.354. PMID 11303086. PMC 1740131. http://oem.bmj.com/cgi/pmidlookup?view=long&pmid=11303086. 
  4. ^ Udani J, Hardy M, Madsen DC (March 2004). "Blocking carbohydrate absorption and weight loss: a clinical trial using Phase 2 brand proprietary fractionated white bean extract". Altern Med Rev 9 (1): 63–9. PMID 15005645. http://www.thorne.com/altmedrev/.fulltext/9/1/63.pdf. 
  5. ^ History of biology 1800–1849
  6. ^ Anselme Payen and Jean-Franois Persoz (1833). "?". Annales de Chimie et de Physique. http://www.anbio.org.br/english/worksh52.htm. 
  7. ^ A History of Fermentation and Enzymes
  8. ^ American Scientist. March-April 2010. 

External links


Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

See also amylase

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Amylase

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Noun

Amylase f.

  1. amylase (type of enzyme)

Simple English

Amylase is an enzyme. It is found in saliva and pancreatic juice. It can break down starch into maltose. It stops working at 60°C.


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