An α-glucosidase which was homogeneous in ultracentrifugal and disc electrophoretic analyses was purified from sugar beet seed by fractionation with ammonium sulfate, chromato-graphy on CM-cellulose and gel filtrations on Bio-Gel P-150. The sedimentation coefficient (S_{20, w}) was calculated to be 5.9S. The molecular weight was estimated to be approximately 9.1×10⁴ by SDS-disc electrophoresis.
The α-glucosidase showed also the pronounced glucoamylase activity. The optimal pH was found to be in the range of 4.1 to 4.7 for both maltose and soluble starch. The enzyme exhibited higher substrate-binding affinity and hydrolytic activity toward soluble starch than toward maltose. The ratio of initial velocity of hydrolysis for maltose (Km, 6.8 mg/ml) and soluble starch (Km, 1.9 mg/ml) was calculated to be 100:120 in this order. The enzyme is an interesting type of α-glucosidase which may be regarded as glucoamylase.

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