amylase(redirected from amylase isoenzymes)
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biological catalyst. The term enzyme comes from zymosis, the Greek word for fermentation, a process accomplished by yeast cells and long known to the brewing industry, which occupied the attention of many 19th-century chemists.
..... Click the link for more information. having physiological, commercial, and historical significance, also called diastase. It is found in both plants and animals. Amylase was purified (1835) from malt by Anselme Payen and Jean Persoz. Their work led them to suspect that similar substances, now known as enzymes, might be involved in biochemical processes. Amylase hydrolyzes starchstarch,
white, odorless, tasteless, carbohydrate powder. It plays a vital role in the biochemistry of both plants and animals and has important commercial uses. In green plants starch is produced by photosynthesis; it is one of the chief forms in which plants store food.
..... Click the link for more information. , glycogenglycogen
, starchlike polysaccharide (see carbohydrate) that is found in the liver and muscles of humans and the higher animals and in the cells of the lower animals. Chemically it is a highly branched condensation polymer of glucose; it is readily hydrolyzed to glucose.
..... Click the link for more information. , and dextrindextrin,
any one of a number of carbohydrates having the same general formula as starch but a smaller and less complex molecule. They are polysaccharides and are produced as intermediate products in the hydrolysis of starch by heat, by acids, and by enzymes.
..... Click the link for more information. to form in all three instances glucoseglucose,
or grape sugar,
monosaccharide sugar with the empirical formula C6H12O6 . This carbohydrate occurs in the sap of most plants and in the juice of grapes and other fruits.
..... Click the link for more information. , maltosemaltose
or malt sugar,
crystalline disaccharide (see carbohydrate). It has the same empirical formula (C12H22O11) as sucrose and lactose but differs from both in structure (see isomer).
..... Click the link for more information. , and the limit-dextrins. Salivary amylase is known as ptyalin; although humans have this enzyme in their saliva, some mammals, such as horses, dogs, and cats, do not. Ptyalin begins polysaccharide digestion in the mouth; the process is completed in the small intestine by the pancreatic amylase, sometimes called amylopsin. The amylase of malt digests barley starch to the disaccharides that are attacked by yeast in the fermentation process.
An enzyme which breaks down (hydrolyzes) starch, the reserve carbohydrate in plants, and glycogen, the reserve carbohydrate in animals, into reducing fermentable sugars, mainly maltose, and reducing nonfermentable or slowly fermentable dextrins. Amylases are classified as saccharifying (β-amylase) and as dextrinizing (α-amylases). The α- and β-amylases are specific for the α- and β-glucosidic bonds which connect the monosaccharide units into large aggregates, the polysaccharides. The α-amylases are found in all types of organs and tissues, whereas β-amylase is found almost exclusively in higher plants. See Carbohydrate, Enzyme, Glycogen, Maltose
In animals the highest concentrations of amylase are found in the saliva and in the pancreas. Salivary amylase is also known as ptyalin and is found in humans, the ape, pig, guinea pig, squirrel, mouse, and rat.
In plants, starch is broken down during the germination of seeds (rich in starch) by associated plant enzymes into sugars. These constitute the chief energy source in the early development of the plant. β-Amylase occurs abundantly in seeds and cereals such as malt. It also is found in yeasts, molds, and bacteria.
any of the enzymes which catalyze the hydrolysis of starches, glycogen, and related polysaccharides by splitting the glucoside bonds between the first and fourth carbon atoms. Three types of amylase are differentiated: alpha-amylase, beta-amylase, and glucoamylase. Alpha-amylase is found in animals, plants, and microorganisms. Reactions in which it participates form mainly dextrins. Beta-amylase, typical in higher plants, catalyzes the formation of maltoses and macromolecular dextrins. Glucoamylase is found in the blood of animals, in fungi, in bacteria, and elsewhere. It catalyzes the formation of glucose and dextrins. Usually hydrolysis of polysaccharides occurs with the simultaneous participation of various amylases. Saccharification of starch by the action of an extract of germinated barley seeds (the fermentative action of amylases) was first described by the Russian academician, K. S. Kirkhgof in 1814. Diastase, the unpurified complex of amylases produced from a malt extract by the French scientists A. Payen and J. Persoz in 1833, was the first enzyme preparation. Some amylases have already been produced in crystalline form. Amylases are specific for various species of organisms. Their physiological role consists in the mobilization of polysaccharide reserves in the cells—for example, in seed germination. Their role in digestion is important; amylases are present in the saliva and in the pancreases of humans and of animals. Microorganisms use starch and excrete amylases into the atmosphere. Alpha-amylase, produced from molds and bacteria, is used for saccharification of starchy brewing mashes in the liquor industry and in breadmaking. Glucoamylase preparations are used to manufacture glucose from starch.
B. B. IURKEVICH