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Classification Although the amylases are designated by different greek letters, they all act on α-1,4 glycosidic bonds. α-Amylase () (CAS β-Amylase () (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 sugar, resulting in the sweet flavor of ripe fruit. Both are present in seeds; β-amylase is present 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 () (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. Acid α-glucosidase Acid α-glucosidase (GAA) () (alternative names: maltase-glucoamylase, MGAM; acid maltase; glucoinvertase; glucosidosucrase; lysosomal α-glucosidase; maltase) is found in the mammalian intestine has similar enzymatic activity to γ-amylase. Deficiencies of this enzyme result in Pompe Disease. Amylase in human physiology Although found in many tissues, amylase is most prominent in pancreatic juice and saliva which each have their 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 (ptyalin) Amylase is found in saliva and breaks starch down into maltose and dextrin. This form is also called ptyalin. Ptyalin will break large, insoluble starch molecules into soluble starches(amylodextrin,erythrodextrin,achrodextrin) producing successively smaller starches and ultimately maltose. Ptyalin acts on linear α(1,4) glucosidic linkages, but compound hydrolysis requires an enzyme which acts on branched products. Salivary amylase is inactivated in the stomach by gastric acid. Optimum conditions for ptyalin Optimum pH - 5.6 - 6.9 Human body temperature - 37 degrees Celsius Presence of certain anions and activators: Chlorine and Bromine - most effective Iodine - less effective Sulfate and Phosphate - least effective The Ptyalin Debate For almost 200 years, medical science has understood that young infant saliva has very low levels of the amylase enzyme ptyalin. This has fuelled an on-going debate by numerous doctors including Chavasse, Sonsino, Tilden, Routh, Husley, Youmans, Dalton, Page, Shelton and Fry; to eliminate farinaceous (starchy) foods from the diet of infants, until full dentition growing of teeth which then coincides with an infant's increased levels of ptyalin. Pancreatic amylase Pancreatic α-amylase randomly cleaves the α(1-4)glycosidic linkages of amylose to yield dextrin, maltose or glucose molecules. It adopts a double displacement mechanism with retention of anomeric configuration. Pompe disease Deficiencies in γ-amylase function result in accumulation of intracellular material. The enzyme is also call acid lysosomal α-glucosidase or acid maltase to reflect the enzymes intracellular function. The condition is known principally as glycogen storage disease, type II or Pompe Disease. Detection The test for amylase is easier to perform than lipase, making it the primary test used to test for and monitor pancreatitis. Labs 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. Unfortunately, because of the small amount present, timing is critical when sampling blood for this measurement. Blood should preferably be taken soon after a bout of pancreatitis pain, otherwise it is excreted rapidly by the kidneys. Interpretation Increased plasma levels in humans are found in: Total amylase readings of over 10X the upper limit of normal (ULN) are suggestive of pancreatitis. 5-10x times the ULN may indicate ileus or duodenal disease or renal failure, and lower elevations are commonly found in salivary gland disease. Notes | |||||||||
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