The action of Balls's crystalline β-amylase is shown to be different from that of amorphous preparations of β-amylase inasmuch as it converts potato amylose to the extent of only 70% into maltose. Evidence is presented that a standard preparation of β-amylase from soya beans contains, in addition to true β-amylase, an enzyme (Z-enzyme) which supplements the β-amylase in effecting the complete conversion of amylose into maltose. It appears that some degree of branching occurs in potato amylose and that this branching impedes the progress of β-amylolysis. The branch links of amylose are different from the α-1 : 6-links of amylopectin and are specifically attacked by Z-enzyme which is without action on the amylopectin branch links. At pH 3.6 the action of Z-enzyme is inhibited.
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