Physicochemical properties of a purified alpha-amylase from the thermophilic fungus Thermomyces lanuginosus

Abstract

The purified alpha-amylase (EC.3.2.1.1) from the thermophilic fungus Thermoyces lanuginosus was investigated in relation to some of its physicochemical properties. The hydrolysis of soluble starch was followed in time as the reduction in the blue-colored complex between starch and iodine and by the production of reducing sugars. Only minor amounts of glucose were detected. The optimum temperature of activity was 60°C, and the optimum pH of activity was between 4.6 and 5.2. The thermostability at 60°C was highest at pH 6.5. When indicated in the range of 50 to 80°C, the alpha-amylase was thermostable at 50°C with half-lives at 60°C of 140 min and at 70°C of 10 min. At 80°C the activity was nil within 5 min. The addition of Ca 2+ had a stabilizing effect on the enzyme which could not be obtained by the addition of Ba 2+, Mg 2+, or Na +. Soluble starch, amylose, and amylopectin were completely degraded by the alpha-amylase, whereas glycogen was hydroylsed to a lesser extent. The amylase inhibitors Trestatin and Acarbose at a concentration of 100 mg l −1 completely inactivated the amylase.