α-Amylase (EC 3.2.1.1) and β-amylase (EC 3.2.1.2) were isolated and purified, each to a state free from contaminating enzymes, from the barley malt and ungerminated barley grains, respectively. Starch granules, isolated from the same sources, served as substrates to study the mode of action of amylases on the digestion of starch granules in vitro. β-Amylase alone had a very small activity on starch granules and formed maltose as a sole digestion product. α-Amylase played a major role in the digestion of starch granules and the combined action of α- and β-amylases was more effective than the action of α-amylase alone, but was less effective, on the same enzyme activity basis, than the crude extract from barley malt, which was thought to represent in vitro the enzyme system for the digestion of starch granules in the germinating barley grains. The possible roles to be played by a debranching enzyme, α-glucosidase and/or glucosyl- or glucanotransferases are discussed.

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