山藥塊莖可溶性酸性蔗糖轉化?之純化及其生化性質的研究

　　　　　基隆山藥塊莖經切片與冷凍乾燥後製成粉末。山藥粉末經由緩衝液抽取、硫酸銨 分劃、Con A-Sepharose親和層析及DEAE-Sephacel離子交換層析等系列步驟純化可溶性酸 性蔗糖轉化□。經由此等步驟純化，可使轉化□純度提高364倍並獲得29%酵素活性回收率。 此純化轉化□水解蔗糖之最適pH為5.0，最適溫度為40~50℃，而Km值為0.033mM，於微酸 性pH貯存時較穩定，鹼性pH(大於8)或高於50℃則不穩定。以膠體過濾法測得分子量為 67kD。此酵素亦可水解棉仔糖(raffinose)但不水解麥芽糖，其水解蔗糖之活性遠高於水解棉 仔糖活性。高濃度蔗糖基質(大於0.2M)對酵素有抑制作用，牛血清白蛋白則對酵素有活化作 用。重金屬離子(1mM)，銅及銀顯著抑制酵素活性而汞則完全抑制酵素活性，因此硫氫基可能 為構成酵素活性中心所必須或位於其附近。
　　　　　Keelong yam tubers were sliced and lyophilized. Acid soluble invertase was purified from the lyophilized powder of yam tubers by means of successive steps of ammonium sulfate fractionation, Con A-Sepharose affinity chromatography and DEAE-Sephacel ion-exchange chromatography. Results showed that the purity of the enzyme increased 364 fold with an activity recovery of 29%. The purified invertase had an optimal pH of 5.0, optimal temperature of 40~50℃ and a Km of 0.033mM for hydrolysis of sucrose. The enzyme was stable for slightly acid pH but unstable for alkaline pH (pH>8) or at temperatures higher than 50℃. The molecular mass of the enzyme as determined from gel filtration was 67kD. The purified enzyme showed activity toward raffinose but no activity toward maltose. However, the activity of sucrose as substrate was much higher than that of raffinose as substrate. Substrate sucrose at high concentrations (above 0.2M) inhibited enzyme activity. Bovine serum albumin activated the enzyme. Heavy metal ions (1mM), Cu□ and Ag□, significantly inhibited activity while Hg□ completely inhibited activity of the enzyme. A sulfhydryl group is probably located at or near the active site of the enzyme.