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.