Biochemical characterization of α-amylase from the yeast Cryptococcus flavus

During our screening of amylolytic microorganisms from Brazilian fruits, we isolated a yeast strain classified as Cryptococcus flavus. When grown on starch-containing medium this strain exhibited the highest amylase production after 24 h of cultivation. The extracellular amylase from C. flavus was purified from the culture broth by a single step using chromatography on a Sephacryl S-100 column. The enzyme was purified 16.14-fold with a yield of 50.21% of the total activity. The purified enzyme was a glycoprotein with an apparent molecular mass of 75 and 84.5 kDa as estimated by sodium dodecyl sulfate–polyacrylamide gel electrophoresis and gel filtration, respectively. The enzyme lost approximately 50% of the molecular mass after treatment with glycosidases. The major end products of starch, amylose, amylopectin, pullulan and glycogen were maltose and maltotriose. The K m value for the pure enzyme was 0.056 mg ml −1 with soluble starch as the substrate. Enzyme activity was optimal at pH 5.5 and 50°C. The enzyme retained 90% of the activity after incubation at 50°C for 60 min and was inhibited by Cu 2+, Fe 2+ and Hg 2+.