Alpha-amylase

Amylase is found in saliva and breaks starch into maltose and dextrin. This form of amylase is also called "ptyalin" /ˈtaɪəlɪn/, which was named by Swedish chemist Jöns Jacob Berzelius. The name derives from the Greek word πτυω (I spit), because the substance was obtained from saliva.[4] It will break large, insoluble starch molecules into soluble starches (amylodextrin, erythrodextrin, and achrodextrin) producing successively smaller starches and ultimately maltose. Ptyalin acts on linear α(1,4) glycosidic linkages, but compound hydrolysis requires an enzyme that 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 37 °C. In contrast, 50% of amylase activity remained after 150 minutes of exposure to gastric juice at pH 4.3.[5] 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.[6]

Optimum pH – 7.0[7]

Human body temperature

Presence of certain anions and activators:

Chloride and bromide – most effective

Iodide – less effective

Sulfate and phosphate – least effective

The salivary amylase gene has undergone duplication during evolution, and DNA hybridization studies indicate 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. Gene copy number is associated with apparent evolutionary exposure to high-starch diets.[8] For example, a Japanese individual had 14 copies of the amylase gene (one allele with 10 copies, and a second allele with four 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 the increased copy number of the salivary amylase gene may have enhanced survival coincident to a shift to a starchy diet during human evolution.

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. In humans, the salivary amylase evolved from a copy of it.[8]

The test for amylase is easier to perform than that for lipase, making it the primary test used to detect and monitor pancreatitis. Medical laboratories 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.

However, because of the small amount present, timing is critical when sampling blood for this measurement. Blood should be taken soon after a bout of pancreatitis pain, otherwise it is excreted rapidly by the kidneys.

Salivary α-amylase has been used as a biomarker for stress[9][10] and as a surrogate marker of sympathetic nervous system (SNS) activity[11] that does not require a blood draw.

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
• Kidney failure – due to reduced excretion

Total amylase readings of over 10 times the upper limit of normal (ULN) are suggestive of pancreatitis. Five to 10 times the ULN may indicate ileus or duodenal disease or kidney failure, and lower elevations are commonly found in salivary gland disease.

• salivary – AMY1A, AMY1B, AMY1C
• pancreatic – AMY2A, AMY2B