Studies on a thermostable α-amylase from the thermophilic fungus Scytalidium thermophilum

An alpha-amylase produced by Scytalidium thermophilum was purified using DEAE-cellulose and CM-cellulose ion exchange chromatography and Sepharose 6B gel filtration. The purified protein migrated as a single band in 6% PAGE and 7% SDS-PAGE. The estimated molecular mass was 36 kDa (SDS-PAGE) and 49 kDa (Sepharose 613). Optima of pH and temperature were 6.0 and 60degreesC, respectively. In the absence of substrate the purified alpha-amylase was stable for 1 h at 50degreesC and had a half-life of 12 min at 60degreesC, but was fully stable in the presence of starch. The enzyme was not activated by several metal ions tested, including Ca2+ (up to 10 mm), but HgCl2 and CuCl2 inhibited its activity. The a-amylase produced by S. thermophilum preferentially hydrolyzed starch, and to a lesser extent amylopectin, maltose, amylose and glycogen in that order. The products of starch hydrolysis (up to 6 h of reaction) analyzed by thin layer chromatography, showed oligosaccharides such as maltotrioses, maltotetraoses and maltopentaoses. Maltose and traces of glucose were formed only after 3 h of reaction. These results confirm the character of the enzyme studied to be an a-amylase (1,4-alpha-glucan glucanohydrolase).