Giorgia Carpegna - Ilaria Quartarone - Vittorio Di Fortunato
DEFINITION
It is 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).
CHEMICAL STRUCTURE AND IMAGES
As diastase, amylase was the first enzyme to be discovered and isolated (by Anselme Payen in 1833). Specific amylase proteins are designated by different Greek letters.
All amylases are glycoside hydrolases and act on α-1,4-glycosidic bonds.
SYNTHESIS AND TURNOVER
It breaks large, insoluble starch molecules into soluble starches (amylodextrin, erythrodextrin, achrodextrin) producing successively smaller starches and ultimately maltose.
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.
Both starch, the substrate for ptyalin, and the product (short chains of glucose) are able to partially protect it against inactivation by gastric acid.
The pancreas also makes amylase to hydrolyse dietary starch into disaccharides and trisaccharides which are converted by other enzymes to glucose to supply the body with energy.
Another form of amylase, β-amylase is synthesized by bacteria, fungi, and plants.
During the ripening of fruit, β -amylase breaks starch into maltose, resulting in the sweet flavor of ripe fruit.
Both β -amylase and α-amylase are present in seeds.
Many microbes also produce amylase to degrade extracellular starches.
An inhibitor of alpha-amylase called phaseolamin has been tested as a potential diet aid.
REGULATION
Α-amylase is synthesized in two different cases:
- During the cefalic fase, for a stimotion of a saliva increse.
- When an hormon called leptin increases the shame of eating; shame of eating it also rilevated in persons with non-insulin dipendendt diabetic. Infact studies have confirmed that amylase activity was higher in diabetics and dicreased with improved glycemic control.
DIAGNOSTIC USE
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.
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.
