Α-Amylase
α-Amylase is the major form of amylase found in humans and other mammals. It is also an enzyme present in seeds which reserves are made of starch, or in fungi (baking yeast for instance). The enzyme cuts alpha-bonds of large sugar molecules.
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 (see AMY1A).
Salivary amylase (ptyalin)
Amylase is found in saliva and breaks starch down into maltose and dextrin. This form of amylase is also called ptyalin. It 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) glycosidic linkages, but compound hydrolysis requires an enzyme which acts on branched products. Salivary amylase is inactivated in the stomach by gastric acid. In gastric juice adjusted to pH 3.3, ptyalin was totally inactivated in 20 minutes at 370C. In contrast, 50% of amylase activity remained after 150 minutes of exposure to gastric juice at pH 4.3.[1]Both starch, the substrate for ptyalin, and the product (short chains of glucose) are able to partially protect it against inactivation by gastric acid. Ptyalin added to buffer at pH 3.0 underwent complete inactivation in 120 minutes; however, addition of starch at a 0.1% level resulted in 10% of the activity remaining, and similar addition of starch to a 1.0% level resulted in about 40% of the activity remaining at 120 minutes.[2]
Optimum conditions for ptyalin
- Optimum pH - 5.6–6.9
- Human body temperature - 37 degrees Celsius
- Presence of certain anions and activators:
Genetic variation in human ptyalin (salivary amylase)
The salivary amylase gene has undergone duplication during evolution, and DNA hybridization studies indicate that many individuals have multiple tandem repeats of the gene. The number of gene copies correlates with the levels of salivary amylase, as measured by protein blot assays using antibodies to human amylase. Perry and coworkers[3] reported that gene copy number is associated with apparent evolutionary exposure to high starch diets. For example, a Japanese individual had 14 copies of the amylase gene (one allele with 10 copies, and a second allele with 4 copies). The Japanese diet has traditionally contained large amounts of rice starch. In contrast, a Biaka individual carried six copies (three copies on each allele). The Biaka are rainforest hunter-gatherers who have traditionally consumed a low starch diet. Perry and colleagues speculated that increased copy number of the salivary amylase gene may have enhanced survival coincident to a shift to a starchy diet during human evolution.
Pancreatic amylase
Pancreatic α-amylase randomly cleaves the α(1-4) glycosidic linkages of amylose to yield dextrin, maltose or maltotriose. It adopts a double displacement mechanism with retention of anomeric configuration.
Amylase in human pathology
The test for amylase is easier to perform than that for lipase, making it the primary test used to detect 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.
Salivary alpha-amylase has been used as a biomarker for stress that does not require a blood draw.[4]
Interpretation
Increased plasma levels in humans are found in:
- Salivary trauma (including anaesthetic intubation).
- Mumps — due to inflammation of the salivary glands.
- Pancreatitis — because of damage to the cells that produce amylase.
- Renal failure — due to reduced excretion.
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.
Genes
Alpha-amylase in grain
Alpha-amylase activity in grain is measured by the Hagberg-Perten Falling Number, a test to assess sprout damages.[5].
Industrial use
Cornstarch is treated with alpha-amylase to produce shorter chains of sugars called oligosaccharides (High-fructose corn syrup).
References
- ^ Fried, M, Abramson, S, Meyer, JH. Passage of salivary amylase through the stomach in humans. Digestive Diseases and Sciences 32:1097-1103 (1987).
- ^ Rosenblum, JL, Irwin, CI, Alpers, DH. Starch and glucose oligosaccharides protect salivary-type amylase activity at acid pH. American Journal of Physiology 254 (Gastrointestinal and Liver Physiology 17):G775-780 (1988).
- ^ Perry, GH, et al. Diet and evolution of human amylase gene copy number variation, Nature Genetics 39:1256-1260 (2007).
- ^ Noto, Yuka (2005). "The Relationship Between Salivary Biomarkers and State-Trait Anxiety Inventory Score Under Mental Arithmetic Stress: A Pilot Study". Anesthesia & Analgesia. 101 (6). United States: Lippincott Williams & Wilkins: 1873–1876. doi:10.1213/01.ANE.0000184196.60838.8D. ISSN 0003-2999. PMID 16301277. Retrieved 2008-03-22.
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External links
- The alpha-Amylase Protein
- alpha-Amylase at the U.S. National Library of Medicine Medical Subject Headings (MeSH)