Change in the Multiple Forms of α-Glucosidase from Spinach Seeds

Two molecular forms of α-glucosidase were isolated from spinach seeds after storage at 4℃ by CM-cellulose column chromatography and gel filtration. The molecular masses of α-glucosidase A and B were 78 kDa and 82 kDa by SDS-PAGE, and 62 kDa and 70 kDa by gel filtration, respectively. α-Glucosidase A had high activity not only toward maltooligosaccharides but also toward α-glucans. The optimum pH was 4.5-5.5 and about 50% of the activity remained after incubation at 65℃ for 20 min. On the other hand, α-glucosidase B had high activity toward maltooligosaccharides but faint activity toward α-glucans. The optimum pH was 5.0 and no activity was found after incubation at 65℃ for 20 min. The enzymatic and immunological properties of α-glucosidase A and B were similar to those of α-glucosidase. Ⅰor Ⅱ, and α-glucosidase Ⅲ or Ⅳ, isolated from spinach seeds without 4℃ storage, respectively. These findings suggest that the α-glucosidase in spinach seeds is modified to be two molecular forms.