The Action Patterns of α‐Amylases

SummaryThe actions of five α‐amylases on amylose, amylopectin and glycogen are described. These are the α‐amylases of human saliva, pig pancreas, barley malt , Aspergillus oryzae and Bacillus subtilis. All these α‐amylases fragment amylose by hydrolysis, the end products being maltose and glucose. Two stages occur in the salivary α‐amylolysis of amylose. The first stage is a rapid hydrolysis to maltose and maltotriose, while in the second stage the latter sugar is slowly hydrolysed to maltose and glucose. Pig‐pancreatic and A. oryzae α‐amylases seem to be similar in their actions to salivary α‐amylase. The retardation of reaction rate in the α‐amylolysis of amylose by malt and B. subtilis α‐amylases occurs at an earlier stage of hydrolysis because of the low affinity of these two enzymes for maltodextrins containing less than about 7 glucose units . Two stages are again apparent in the hydrolysis of amylopectin and glycogen by salivary α‐amylase. As well as the sugars also formed from amylose there are present α‐limit dextrins containing the α‐1:6‐branch linkages of the polysaccharides as well as α‐1:4‐linkages. Some of these dextrins are further hydrolysed in the second stage of the reaction. It is apparent that certain α‐1:4‐bonds in the vicinity of the branch point are resistant to amylolysis. Pig‐pancreatic and A. oryzae α‐amylases form the same second‐stage α‐limit dextrins, the smallest of which is a tetrasaccharide. Malt α‐amylase gives a trisaccharide, panose, as the smallest such dextrin, while B. subtilis α‐amylase forms a pentasaccharide . A hypothesis is put forward to explain the formation of the α‐limit dextrins by salivary α‐amylase .