ACTIVATION, PURIFICATION AND PROPERTIES OF BETA-AMYLASE FROM SWEET-POTATOES (IPOMOEA-BATATAS)

On storage at room temperature or when treated with ethylene, beta-amy lase activity in tubers of sweet potato (Ipomoea batatas) increased si gnificantly. Three starch-degradation amylases were found in the crude extract of sweet-potato varieties Tainung No. 57 and Chailai when ana lysed by gel electrophoresis and amylase activity staining. One of the amylases was identified as beta-amylase. beta-Amylases were purified from the crude extract of sweet-potato varieties Tainung No. 57 and Ch ailai by sequential steps of heat treatment, change of pH, (NH4)(2)SO4 fractionation and Sephacryl S-400 HR gel filtration. By these steps, both purified beta-amylases were homogeneous, with yields as high as 7 3-76%. Both beta-amylases had an optimal pH of 5, an optimal temperatu re of 50 degrees C, and were rather stable at 60 degrees C. The molecu lar masses of the beta-amylases were 209 kDa for Tainung No. 57 and 23 9 kDa for Chailai, as determined by gel filtration. Heavy-metal ions ( 0.5 mM), Cu2+, Hg2+ 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 co ncentrations also inhibited the activity of beta-amylase from the Tain ung No. 57 variety of sweet potato.