Amylase

Amylase is a digestive enzyme classified as a saccharidase (an enzyme that cleaves polysaccharides). It is mainly a constituent of pancreatic juice and saliva, needed for the breakdown of long-chain carbohydrates (such as starch) into smaller units.

Amylase is a digestive enzyme made primarily by the pancreas and salivary glands. Enzymes are substances made and used by the body to trigger specific chemical reactions. The primary function of the enzyme amylase is to break down starches in food so that they can be used by the body. Amylase is also synthesised in the fruit of plants during ripening, causing them to become sweeter.

Amylases are enzymes that catalyze the hydrolysis of alpha-1, 4-glycosidic linkages of polysaccharides to yield dextrins, oligosaccharides, maltose and D-glucose. Amylases are derived from animal, fungal and plant sources. Pancreatin and pancrelipase contain amylase derived from the pancreas of animals, usually porcine pancreas. Amylase is also derived from barley malt and the fungus Aspergillus oryzae. There are a few different amylases. These enzymes are classified according to the manner in which the glysosidic bond is attacked. Alpha-amylases hydrolyze alpha-1, 4-glycosidic linkages, randomly yielding dextrins, oligosaccharides and monosaccharides. Alpha-amylases are endo- amylases. Exoamylases hydrolyze the alpha-1, 4-glycosidic linkage only from the non-reducing outer polysaccharide chain ends. Exoamylases include beta-amylases and glucoamylases (gamma-amylases, amyloglucosidases). Beta-amylases yield beta-limit dextrins and maltose. Gamma-amylases yield glucose. Amylases are used as digestants.

Amylase is a calcium dependent enzyme which hydrolyzes complex carbohydrates at alpha 1,4-linkages to form maltose and glucose. Amylase is filtered by renal tubules and resorbed (inactivated) by tubular epithelium. Active enzyme does not appear in urine. Small amounts of amylase are taken up by Kupffer cells in the liver. In healthy dogs, 14% of amylase is bound to globulins. Because of this polymerization, canine amylase has variable (high) molecular weights and is not normally filtered by the kidney. In dogs with renal disease, this polymerized (macroamylase) amylase is found in higher concentration (from 5-62% of total amylase activity) and contributes to the hyperamylasemia seen in these disorders. There are 4 different isoenzymes of amylase in the dog: isoenzyme 3 is found in the pancreas (>50%), whereas isoenzyme 4 is found in all tissues. a-Amylase catalyzes the hydrolysis of internal (endoglycosidase) a-1,4-glucan links in polysaccharides containing 3 or more a-1,4-linked D-glucose units (amylose and amylopectin) yielding a mixture of maltose and glucose. Both of these monosaccharides can then be converted to about 30 ATP units of energy by encountering the glycolysis mechanism and the citric acid cycle. Both amylose and amylopectin are examples of polysaccharides, that is, polymers made of many sugar units. Both are composed entirely of glucose monomers. Amylose is a straight chain polymer of glucose units bonded by a-1,4 glycosidic linkages. This means that neighboring glucose units are joined from the C1 carbon of one to the C4 carbon of the other, the bond having an orientation referred to as alpha. Amylopectin is a branched chain molecule. The glucose units in amylopectin are bonded in the same manner as in amylose, except for the branch points where the chains are joined by a-1,6 glycosidic linkages. Amylose composes from 20 to 30% of starch. Amylopectin comprises the remaining 70 to 80%, and because of its branching, is less soluble and more viscous than amylose.

Alpha-Amylase (1,4-a-D-glucan glucanohydrolase) in animals are monomeric, calcium-binding proteins that are present in both salivary and pancreatic secretions. In the gastrointestinal tract, it is a digestive enzyme that is secreted into the Duodenum where it starts to degrade (hydrolyze) the a-1,4 glucosidic linkages of starch to maltose and maltotriose. a-Amylases are used to hydrolyze glycogen, the reserve carbohydrates in animals, when the blood glucose levels are low. Salivary amylase, a major component of human salivary secretions, possesses multiple functions in the oral cavity. It is the only enzyme in the saliva capable of degrading oligosaccharides, which are used by the oral microflora for nutritional purposes. The structural neighbor, b-amylase, breaks down starch during the germination of seeds (rich in starch) into sugars. These sugars constitute the chief energy source in the early development of the plant. b-Amylase is able to break down the a-1,4 linkages of starch polymers in plants and seeds.

Amylase is also used in industry. It is used in brewing and fermentation industries for the conversion of starch to fermentable sugars, in the textile industry for designing textiles, in the laundry industry in a mixture with protease and lipase to launder clothes, in the paper industry for sizing, and in the food industry for preparation of sweet syrups, to increase diastase content of flour, for modification of food for infants, and for the removal of starch in jelly production.

The pancreas has the highest amylase concentration and largest total amount of amylase of any organ in the body. Unfortunately, other tissues, particularly the parotid salivary glands, also contain large quantities. Pancreatic or salivary amylase is not absorbed by intact gut mucosa, and normal serum amylase activity levels are low. Any amylase that is present presumably comes from enzyme leakage directly into the blood from the ascinar cells or via lymphatics draining the glands. With ductular obstruction and/or inflammation of either the pancreas or parotid glands, enzyme leakage directly into the blood or via the lymphatics increases. In rare situations gut permeability changes, whereby a large quantitiy of amylase leaks into the peritoneal fluid and is eventually delivered via thoracic duct into the circulation causing hyperamylasemia. When amylase levels are too high in the urine and someone has abdominal pain then they are automatically diagnosed with pancreatitis.

The major role of the calcium-containing metalloenzyme amylase in the oral cavity is the hydrolysis of the alpha-1,4 linkages of starch. Amylase can play an important role in the colonization and metabolism of oral bacteria leading to dental plaque formation. Amylase bound to the bacterial surface retains its enzymatic activity. The bacterial-bound amylase can hydrolyze starch to glucose, which is then metabolized to lactic acid by the bacteria, thereby leading to dental plaque formation and progression.

Amylase research information

Starch hydrolysis by amylase
A test to measure the amount of amylase in serum (blood)
The effect of pH on enzyme activity - salivary amylase and starch digestion
Specificity of enzymes - digestion of starch by amylase
Amylase assay, organ specificity, causes of hyperamylasemia
Purification of salivary alpha amylase
Enzyme activity: pancreatic amylase
Amylase-treated rice flour oral rehydration solution with enhanced energy density
Characterization of sweet-Potato beta-amylase