Microorganisms, higher plants, and animals produce a large number of different protein inhibitors of a-amylases in order to regulate the activity of these enzymes. These inhibitors can be grouped into six classes based on their tertiary structures: lectin-like, knottin-like, cereal-type, Kunitz-like, γ-purothionin-like and thaumatin-like inhibitors. Some of these inhibitors act by directly blocking the active centre of the enzyme at various local sites.
In animals, a-amylase inhibitors reduce the glucose peaks that can occur after a meal, slowing the speed with which a-amylase can convert starch to simple sugars until the body can deal with it. This is of particular importance in people with diabetes, where low insulin levels prevent extracellular glucose from being cleared quickly from the blood. Therefore, diabetics tend to have low a-amylase levels in order to keep glucose levels under control, except after taking insulin, which causes a rise in pancreatic a-amylase.
Plants also use a-amylase inhibitors as a defence strategy. These inhibitors impede the digestive action of a-amylases and proteinases in the insect gut, thereby acting as insect anti-feedants. As a result, a-amylase inhibitors have potential in various fields, including crop protection and the treatment of diabetes.
Amylases have found several valuable niches within our society, some of which are listed below:
A simple test can be used to determine the level of amylases present in blood plasma in order to screen for pancreatitis. The test is usually performed soon after a bout of pancreatic pain, as the kidneys rapidly excrete amylases. Increased levels of amylases occur during pancreatitis as a result of the damage that is done to amylase-producing cells, but levels can also be elevated due to renal failure (reduced excretion) or mumps (inflammation of salivary glands).
Amylases are synthesized in the fruits of many plants during ripening, causing them to become sweeter as the starch is degraded to sugars.
Amylases are produced during the germination of cereal grains, and this enzyme is key to the production of malt.
a-Amylases are added to dough as part of a flour improver in order to hydrolyze the starch present in the flour to provide more fermentable sugars for the yeast, which decreases rising times, and ultimately costs. In addition, the use of different enzymes can alter the properties of the flour.