Isolation and Functional Properties of Amylolytic Enzyme and α-D-Galactose- binding Lectin from Bulbils of Yam (Dioscorea japonica Thumb)

Abstract

In a course of research on chemical properties and functions of Japanese traditional plant foods, our interests were drawn to “Mukago”, bulbils of Japanese yam, Dioscorea japonica Thumb., since our preliminary study indicated that it contains α-galactose-recognizing lectin (α-Gal-Lec) beside unique amylolytic enzyme(s).

Fresh Mukago was homogenized in PBS at cold. After removal of starch, protein was precipitated with ammonium sulfate(0.6 sat.), which was fractionated using affinity chromatographic techniques, involving β-cyclodextrin (CD) for α-amylolytic enzyme, and α-Galactose-conjugate column for a specific lectin, respectively. The purified α-Gal-Lec, showing a single band on SDS PAGE(38 kDa) was a dimeric molecule. This lectin interacted with various α-Gal-containing polysaccharides, e.g.plant galactomannans and also human blood type B substance, but not type A. Thus, chemical and binding properties of α-Gal-Lec appeared resemble to that of arrow-head tuber. The amylolytic enzyme, purified through β-CD was homogenous on SDS PAGE(31 kDa). Its action pattern on starch was appeared an intermediate manner of salivary (or bacterial) and funji (Takaamylase) types. It readily hydrolyzes Mukago starch, which might contain rather short α-1, 4 linked branches.