The fungal strain Mortierella alliacea YN-15 is an arachidonic acid producer that assimilates soluble starch despite having undetectable α-amylase activity. Here, a α-glucosidase responsible for the starch hydrolysis was purified from the culture broth through four-step column chromatography. Maltose and other oligosaccharides were less preferentially hydrolyzed and were used as a glucosyl donor for transglucosylation by the enzyme, demonstrating distinct substrate specificity as a fungal α-glucosidase. The purified enzyme consisted of two heterosubunits of 61 and 31 kDa that were not linked by a covalent bond but stably aggregated to each other even at a high salt concentration (0.5 M), and behaved like a single 92-kDa component in gel-filtration chromatography. The hydrolytic activity on maltose reached a maximum at 55°C and in a pH range of 5.0-6.0, and in the presence of ethanol, the transglucosylation reaction to form ethyl-α-D-glucoside was optimal at pH 5.0 and a temperature range of 45-50°C.
真菌菌株Mortierella alliacea YN-15是一种能利用
可溶性淀粉生产
花生四烯酸的菌株,尽管其
α-淀粉酶活性无法检测到。在此,通过四步柱层析从培养液中纯化出一种负责淀粉
水解的α-
葡萄糖苷酶。该酶对
麦芽糖和其他低聚糖的
水解优先性较低,但能将其作为
葡萄糖供体进行转
葡萄糖基作用,显示出作为真菌α-
葡萄糖苷酶的独特底物特异性。纯化的酶由两个分别为61和31 kDa的异亚基组成,它们之间没有通过共价键连接,但在高盐浓度(0.5 M)下稳定地聚集在一起,在凝胶过滤层析中表现出如同一个92 kDa组分的特性。该酶对
麦芽糖的
水解活性在55°C和pH 5.0-6.0范围内达到最大,并且在存在
乙醇的情况下,形成乙基-α-
D-葡萄糖苷的转
葡萄糖基反应在pH 5.0和温度范围45-50°C时最优。