Amylase (EC 3.2.1.1) 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 also synthesized in the fruit of many plants during ripening, causing them to become sweeter, and also during the germination of cereal grains. Grain amylase is key to the production of malt.

Types

There are two isoforms of amylase: pancreatic and salivary amylase. They behave differently on isoelectric focusing, and can also be separated in testing by using specific monoclonal antibodies.

Ptyalin

Ptyalin is the name given to the amylase found in saliva that breaks starch down into maltose and dextrin.

Function

Alpha-amylase cleaves the α(1-4)glycosidic linkages of amylose to yield maltose molecules (disaccharides of α-glucose).

Genetics

In humans, all amylase isoforms link to chromosome 1q21.

Detection

The test for amylase is easy to perform and has been the main test for 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:

• Salivary trauma (including aneasthetic 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.