Amylase

Figure 1. Model of ptyalin (human salivary alpha-amylase).

Amylase is a class of enzymes that catalyse the hydrolysis of starch molecules into smaller carbohydrate molecules. (Hydrolysis is the splitting of a compound molecule by the addition of water molecules.) There are three categories of amylases: alpha-, beta-, and gamma-amylase, so defined based on the way they attach the bonds of starch molecules.

The Alpha-amylase is widespread among living organisms. The Alpha-amylase ptyalin is produced by the salivary glands, whereas pancreatic amylase is secreted by the pancreas into the small intestine. Although food remains in the mouth for only a short time, the action of ptyalin continues for up to several hours in the stomach. Under optimal conditions between 30-40% of starches can be broken down to maltose in the stomach. When food is passed into the small intestine, the remainder of the starch molecules are catalysed mainly to maltose by pancreatic amylase.

Beta-amylase is not produced in human bodies. Beta-amylases are present in yeasts, mold, bacteria, and plants, particularly in seeds. They are the principal components of a mixture called diastase that is used in the conversion of cereal grains to fermentable sugars.

Like alpha-amylase, gamma-amylase is produced in human bodies. Gamma-amylases are known for their efficiency in cleaving certain types of glycosidic linkages in acidic environments and operate in the stomach.