Multiple Molecular Forms ofα-Glucosidase from Spinach Seeds,Spinacia oleraceaL.

Four molecular forms of α-glucosidase were isolated from spinach seeds by several kinds of chromatography. The molecular masses of α-glucosidases I, II, III, and IV were 78, 78, 82, and 82 kDa by SOS–PAGE, and 62, 62, 190, and 70 kDa by gel filtration, respectively. α-Glucosidases I and II showed similar enzymatic properties, in which the Km for soluble starch was about 10 times lower than that for maltose, and they had higher activity not only toward malto-oliosaccharides but also toward α-glucans. The optimum pH was 4.5–5.5 and about 50% of the activity remained after incubation at 70°C for 20 min. On the other hand, α-glucosidases III and IV showed similar enzymatic properties, in which the Km for maltose was 3–4 times lower than that for soluble starch, and they had high activity toward malto-oligosaccharides but faint activity toward α-glucans. The optimum pH was 4.5–5.0 and no activity was found after incubation at 70°C for 20 min. However, anti-α-glucosidase III serum formed precipitation specifica...