Activation, purification and properties of beta-amylase from sweet potatoes (Ipomoea batatas)

Abstract

On storage at room temperature or when treated with ethylene, β-amylase activity in tubers of sweet potato (Ipomoea batatas) increased significantly. Three starch-degradation amylases were found in the crude extract of sweet-potato varieties Tainung No. 57 and Chailai when analysed by gel electrophoresis and amylase activity staining. One of the amylases was identified as β-amylase. β-Amylases were purified from the crude extract of sweet-potato varieties Tainung No. 57 and Chailai by sequential steps of heat treatment, change of pH, (NH 4 ) 2 SO 4 fractionation and Sephacryl S-400 HR gel filtration. By these steps, both purified β-amylases were homogeneous, with yields as high as 73-76%. Both β-amylases had an optimal pH of 5, an optimal temperature of 50°C, and were rather stable at 60°C. The molecular masses of the β-amylases were 209 kDa for Tainung No. 57 and 239 kDa for Chailai, as determined by gel filtration. Heavy-metal ions (0.5 mM), Cu 2+ , Hg 2+ and Ag + , and chemical modification agents, PMSF (2 mM), p-hydroxymercuribenzoic acid (0.4 mM) and N-bromosuccinimide (0.4 mM) significantly inhibited the enzyme activities. Starch at high concentrations also inhibited the activity of β-amylase from the Tainung No. 57 variety of sweet potato.