溫度對甘藷β-澱粉酶活性影響之研究

Abstract

β-澱粉酶(β-amylase, EC 3.2.1.2，簡稱BA) 催化水解澱粉鏈之非還原端 α-1,4-糖甙鍵，釋出β-maltose而留下β-limit dextrin，分類上屬於外切澱粉酶。 本論文針對不同品種之甘藷測定BA活性，選擇總活性最高之60℃樣本與對照組進行純化，測定生化性質加以比較，來探討溫度對BA活性之影響。純化將粗抽液經硫酸銨100%沈澱後，進行製備式電泳可得到相當純的BA。 對照組與60℃樣本對基質澱粉之 Km 值分別為 6.02 與 2.95%。酵素最適反應溫度均為60℃，對照組最適反應pH為 5，60℃樣本為 4.5。對照組與 60℃樣本之活化能分別為 3.35 與 4.2 kcal/mol；酵素活性會受到汞、銅、銀離子的抑制，除了汞離子外，60℃樣本對金屬離子的耐受性均較對照組差。化學修飾劑β-mercaptoethanol、DTT、PMSF中除了DTT外，60℃樣本受到的影響較對照組來得大。

β-amylase (EC 3.2.1.2) is an exoamylase that releases successive maltose units from the nonreducing end of a polysaccharide chain by hydrolyzing of α-1,4-glucan linkages. In this article, BA activities were measured in different varieties of sweet potato, and chose the highest total activity sample under 60℃ treatment and control sample to purify. And put to compare their biochemical characteristics and the effects of temperature on BA activity. Crude extraction precipitated by ammonium sulfate 100% then run preparative electrophoresis can get pure enzyme. Km values for starch substrate of control sample and 60℃ sample were estimated to be 6.02 and 2.95%, respectively. Optimal temperature for both samples are 60℃. Optimal pH value for control sample is 5, and for 60℃ sample is 4.5. Activation energy for control sample and 60℃ sample is 3.35 and 4.2 kcal/mol, respectively. BA activity could be inhibited by Hg2+, Cu2+ and Ag+. Except for Hg2+, tolerance to metal ions of 60℃ sample is less than control sample. Chemical modified reagents, including β-mercaptoethanol, DTT, PMSF also influence BA activity. Except for DTT, influence of chemical modified reagents of 60℃ sample is more than control sample.